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> 14. Input-Output Input-output is provided in the language by means of predefined packages. The generic packages SEQUENTIAL_IO and DIRECT_IO define input-output operations applicable to files containing elements of a given type. Additional operations for text input-output are supplied in the package TEXT_IO. The package IO_EXCEPTIONS defines the exceptions needed by the above three packages. Finally, a package LOW_LEVEL_IO is provided for direct control of peripheral devices. References: direct_io package 14.2 14.2.4, io_exceptions package 14.5, low_level_io package 14.6, sequential_io package 14.2 14.2.2, text_io package 14.3 > 14.1 External Files and File Objects Values input from the external environment of the program, or output to the environment, are considered to occupy external files. An external file can be anything external to the program that can produce a value to be read or receive a value to be written. An external file is identified by a string (the name). A second string (the form) gives further system-dependent characteristics that may be associated with the file, such as the physical organization or access rights. The conventions governing the interpretation of such strings must be documented in Appendix F. Input and output operations are expressed as operations on objects of some file type, rather than directly in terms of the external files. In the remainder of this chapter, the term file is always used to refer to a file object; the term external file is used otherwise. The values transferred for a given file must all be of one type. Input-output for sequential files of values of a single element type is defined by means of the generic package SEQUENTIAL_IO. The skeleton of this package is given below. with IO_EXCEPTIONS; generic type ELEMENT_TYPE is private; package SEQUENTIAL_IO is type FILE_TYPE is limited private; type FILE_MODE is (IN_FILE, OUT_FILE); ... procedure OPEN (FILE : in out FILE_TYPE; ...); ... procedure READ (FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE); procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE); ... end SEQUENTIAL_IO; In order to define sequential input-output for a given element type, an instantiation of this generic unit, with the given type as actual parameter, must be declared. The resulting package contains the declaration of a file type (called FILE_TYPE) for files of such elements, as well as the operations applicable to these files, such as the OPEN, READ, and WRITE procedures. Input-output for direct access files is likewise defined by a generic package called DIRECT_IO. Input-output in human-readable form is defined by the (nongeneric) package TEXT_IO. Before input or output operations can be performed on a file, the file must first be associated with an external file. While such an association is in effect, the file is said to be open, and otherwise the file is said to be closed. The language does not define what happens to external files after the completion of the main program (in particular, if corresponding files have not been closed). The effect of input-output for access types is implementation-dependent. An open file has a current mode, which is a value of one of the enumeration types type FILE_MODE is (IN_FILE, INOUT_FILE, OUT_FILE); -- for DIRECT_IO type FILE_MODE is (IN_FILE, OUT_FILE); -- for SEQUENTIAL_IO and TEXT_IO These values correspond respectively to the cases where only reading, both reading and writing, or only writing are to be performed. The mode of a file can be changed. Several file management operations are common to the three input-output packages. These operations are described in section 14.2.1 for sequential and direct files. Any additional effects concerning text input-output are described in section 14.3.1. The exceptions that can be raised by a call of an input-output subprogram are all defined in the package IO_EXCEPTIONS; the situations in which they can be raised are described, either following the description of the subprogram (and in section 14.4), or in Appendix F in the case of error situations that are implementation-dependent. Notes: Each instantiation of the generic packages SEQUENTIAL_IO and DIRECT_IO declares a different type FILE_TYPE; in the case of TEXT_IO, the type FILE_TYPE is unique. A bidirectional device can often be modeled as two sequential files associated with the device, one of mode IN_FILE, and one of mode OUT_FILE. An implementation may restrict the number of files that may be associated with a given external file. The effect of sharing an external file in this way by several file objects is implementation-dependent. References: create procedure 14.2.1, current index 14.2, current size 14.2, delete procedure 14.2.1, direct access 14.2, direct file procedure 14.2, direct_io package 14.1 14.2, enumeration type 3.5.1, exception 11, file mode 14.2.3, generic instantiation 12.3, index 14.2, input file 14.2.2, io_exceptions package 14.5, open file 14.1, open procedure 14.2.1, output file 14.2.2, read procedure 14.2.4, sequential access 14.2, sequential file 14.2, sequential input-output 14.2.2, sequential_io package 14.2 14.2.2, string 3.6.3, text_io package 14.3, write procedure 14.2.4 > 14.2 Sequential and Direct Files Two kinds of access to external files are defined: sequential access and direct access. The corresponding file types and the associated operations are provided by the generic packages SEQUENTIAL_IO and DIRECT_IO. A file object to be used for sequential access is called a sequential file, and one to be used for direct access is called a direct file. For sequential access, the file is viewed as a sequence of values that are transferred in the order of their appearance (as produced by the program or by the environment). When the file is opened, transfer starts from the beginning of the file. For direct access, the file is viewed as a set of elements occupying consecutive positions in linear order; a value can be transferred to or from an element of the file at any selected position. The position of an element is specified by its index, which is a number, greater than zero, of the implementation-defined integer type COUNT. The first element, if any, has index one; the index of the last element, if any, is called the current size; the current size is zero if there are no elements. The current size is a property of the external file. An open direct file has a current index, which is the index that will be used by the next read or write operation. When a direct file is opened, the current index is set to one. The current index of a direct file is a property of a file object, not of an external file. All three file modes are allowed for direct files. The only allowed modes for sequential files are the modes IN_FILE and OUT_FILE. References: count type 14.3, file mode 14.1, in_file 14.1, out_file 14.1 > 14.2.1 File Management The procedures and functions described in this section provide for the control of external files; their declarations are repeated in each of the three packages for sequential, direct, and text input-output. For text input-output, the procedures CREATE, OPEN, and RESET have additional effects described in section 14.3.1. procedure CREATE(FILE : in out FILE_TYPE; MODE : in FILE_MODE := DEFAULT_MODE; NAME : in STRING := ""; FORM : in STRING := ""); Establishes a new external file, with the given name and form, and associates this external file with the given file. The given file is left open. The current mode of the given file is set to the given access mode. The default access mode is the mode OUT_FILE for sequential and text input-output; it is the mode INOUT_FILE for direct input-output. For direct access, the size of the created file is implementation-dependent. A null string for NAME specifies an external file that is not accessible after the completion of the main program (a temporary file). A null string for FORM specifies the use of the default options of the implementation for the external file. The exception STATUS_ERROR is raised if the given file is already open. The exception NAME_ERROR is raised if the string given as NAME does not allow the identification of an external file. The exception USE_ERROR is raised if, for the specified mode, the environment does not support creation of an external file with the given name (in the absence of NAME_ERROR) and form. procedure OPEN(FILE : in out FILE_TYPE; MODE : in FILE_MODE; NAME : in STRING; FORM : in STRING := ""); Associates the given file with an existing external file having the given name and form, and sets the current mode of the given file to the given mode. The given file is left open. The exception STATUS_ERROR is raised if the given file is already open. The exception NAME_ERROR is raised if the string given as NAME does not allow the identification of an external file; in particular, this exception is raised if no external file with the given name exists. The exception USE_ERROR is raised if, for the specified mode, the environment does not support opening for an external file with the given name (in the absence of NAME_ERROR) and form. procedure CLOSE(FILE : in out FILE_TYPE); Severs the association between the given file and its associated external file. The given file is left closed. The exception STATUS_ERROR is raised if the given file is not open. procedure DELETE(FILE : in out FILE_TYPE); Deletes the external file associated with the given file. The given file is closed, and the external file ceases to exist. The exception STATUS_ERROR is raised if the given file is not open. The exception USE_ERROR is raised if (as fully defined in Appendix F) deletion of the external file is not supported by the environment. procedure RESET(FILE : in out FILE_TYPE; MODE : in FILE_MODE); procedure RESET(FILE : in out FILE_TYPE); Resets the given file so that reading from or writing to its elements can be restarted from the beginning of the file; in particular, for direct access this means that the current index is set to one. If a MODE parameter is supplied, the current mode of the given file is set to the given mode. The exception STATUS_ERROR is raised if the file is not open. The exception USE_ERROR is raised if the environment does not support resetting for the external file and, also, if the environment does not support resetting to the specified mode for the external file. function MODE(FILE : in FILE_TYPE) return FILE_MODE; Returns the current mode of the given file. The exception STATUS_ERROR is raised if the file is not open. function NAME(FILE : in FILE_TYPE) return STRING; Returns a string which uniquely identifies the external file currently associated with the given file (and may thus be used in an OPEN operation). If an environment allows alternative specifications of the name (for example, abbreviations), the string returned by the function should correspond to a full specification of the name. The exception STATUS_ERROR is raised if the given file is not open. function FORM(FILE : in FILE_TYPE) return STRING; Returns the form string for the external file currently associated with the given file. If an environment allows alternative specifications of the form (for example, abbreviations using default options), the string returned by the function should correspond to a full specification (that is, it should indicate explicitly all options selected, including default options). The exception STATUS_ERROR is raised if the given file is not open. function IS_OPEN(FILE : in FILE_TYPE) return BOOLEAN; Returns TRUE if the file is open (that is, if it is associated with an external file), otherwise returns FALSE. References: current mode 14.1, current size 14.1, closed file 14.1, direct access 14.2, external file 14.1, file 14.1, file_mode type 14.1, file_type type 14.1, form string 14.1, inout_file 14.2.4, mode 14.1, name string 14.1, name_error exception 14.4, open file 14.1, out_file 14.1, status_error exception 14.4, use_error exception 14.4 > 14.2.2 Sequential Input-Output The operations available for sequential input and output are described in this section. The exception STATUS_ERROR is raised if any of these operations is attempted for a file that is not open. procedure READ(FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE); Operates on a file of mode IN_FILE. Reads an element from the given file, and returns the value of this element in the ITEM parameter. The exception MODE_ERROR is raised if the mode is not IN_FILE. The exception END_ERROR is raised if no more elements can be read from the given file. The exception DATA_ERROR is raised if the element read cannot be interpreted as a value of the type ELEMENT_TYPE; however, an implementation is allowed to omit this check if performing the check is too complex. procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE); Operates on a file of mode OUT_FILE. Writes the value of ITEM to the given file. The exception MODE_ERROR is raised if the mode is not OUT_FILE. The exception USE_ERROR is raised if the capacity of the external file is exceeded. function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; Operates on a file of mode IN_FILE. Returns TRUE if no more elements can be read from the given file; otherwise returns FALSE. The exception MODE_ERROR is raised if the mode is not IN_FILE. References: data_error exception 14.4, element 14.1, element_type 14.1, end_error exception 14.4, external file 14.1, file 14.1, file mode 14.1, file_type 14.1, in_file 14.1, mode_error exception 14.4, out_file 14.1, status_error exception 14.4, use_error exception 14.4 > 14.2.3 Specification of the Package Sequential_IO with IO_EXCEPTIONS; generic type ELEMENT_TYPE is private; package SEQUENTIAL_IO is type FILE_TYPE is limited private; type FILE_MODE is (IN_FILE, OUT_FILE); -- File management procedure CREATE(FILE : in out FILE_TYPE; MODE : in FILE_MODE := OUT_FILE; NAME : in STRING := ""; FORM : in STRING := ""); procedure OPEN (FILE : in out FILE_TYPE; MODE : in FILE_MODE; NAME : in STRING; FORM : in STRING := ""); procedure CLOSE (FILE : in out FILE_TYPE); procedure DELETE(FILE : in out FILE_TYPE); procedure RESET (FILE : in out FILE_TYPE; MODE : in FILE_MODE); procedure RESET (FILE : in out FILE_TYPE); function MODE (FILE : in FILE_TYPE) return FILE_MODE; function NAME (FILE : in FILE_TYPE) return STRING; function FORM (FILE : in FILE_TYPE) return STRING; function IS_OPEN(FILE : in FILE_TYPE) return BOOLEAN; -- Input and output operations procedure READ (FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE); procedure WRITE (FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE); function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; -- Exceptions STATUS_ERROR : exception renames IO_EXCEPTIONS.STATUS_ERROR; MODE_ERROR : exception renames IO_EXCEPTIONS.MODE_ERROR; NAME_ERROR : exception renames IO_EXCEPTIONS.NAME_ERROR; USE_ERROR : exception renames IO_EXCEPTIONS.USE_ERROR; DEVICE_ERROR : exception renames IO_EXCEPTIONS.DEVICE_ERROR; END_ERROR : exception renames IO_EXCEPTIONS.END_ERROR; DATA_ERROR : exception renames IO_EXCEPTIONS.DATA_ERROR; private -- implementation-dependent end SEQUENTIAL_IO; References: close procedure 14.2.1, create procedure 14.2.1, data_error exception 14.4, delete procedure 14.2.1, device_error exception 14.4, end_error exception 14.4, end_of_file function 14.2.2, file_mode 14.1, file_type 14.1, form function 14.2.1, in_file 14.1, io_exceptions 14.4, is_open function 14.2.1, mode function 14.2.1, mode_error exception 14.4, name function 14.2.1, name_error exception 14.4, open procedure 14.2.1, out_file 14.1, read procedure 14.2.2, reset procedure 14.2.1, sequential_io package 14.2 14.2.2, status_error exception 14.4, use_error exception 14.4, write procedure 14.2.2, > 14.2.4 Direct Input-Output The operations available for direct input and output are described in this section. The exception STATUS_ERROR is raised if any of these operations is attempted for a file that is not open. procedure READ(FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE; FROM : in POSITIVE_COUNT); procedure READ(FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE); Operates on a file of mode IN_FILE or INOUT_FILE. In the case of the first form, sets the current index of the given file to the index value given by the parameter FROM. Then (for both forms) returns, in the parameter ITEM, the value of the element whose position in the given file is specified by the current index of the file; finally, increases the current index by one. The exception MODE_ERROR is raised if the mode of the given file is OUT_FILE. The exception END_ERROR is raised if the index to be used exceeds the size of the external file. The exception DATA_ERROR is raised if the element read cannot be interpreted as a value of the type ELEMENT_TYPE; however, an implementation is allowed to omit this check if performing the check is too complex. procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE; TO : in POSITIVE_COUNT); procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE); Operates on a file of mode INOUT_FILE or OUT_FILE. In the case of the first form, sets the index of the given file to the index value given by the parameter TO. Then (for both forms) gives the value of the parameter ITEM to the element whose position in the given file is specified by the current index of the file; finally, increases the current index by one. The exception MODE_ERROR is raised if the mode of the given file is IN_FILE. The exception USE_ERROR is raised if the capacity of the external file is exceeded. procedure SET_INDEX(FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); Operates on a file of any mode. Sets the current index of the given file to the given index value (which may exceed the current size of the file). function INDEX(FILE : in FILE_TYPE) return POSITIVE_COUNT; Operates on a file of any mode. Returns the current index of the given file. function SIZE(FILE : in FILE_TYPE) return COUNT; Operates on a file of any mode. Returns the current size of the external file that is associated with the given file. function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; Operates on a file of mode IN_FILE or INOUT_FILE. Returns TRUE if the current index exceeds the size of the external file; otherwise returns FALSE. The exception MODE_ERROR is raised if the mode of the given file is OUT_FILE. References: count type 14.2, current index 14.2, current size 14.2, data_error exception 14.4, element 14.1, element_type 14.1, end_error exception 14.4, external file 14.1, file 14.1, file mode 14.1, file_type 14.1, in_file 14.1, index 14.2, inout_file 14.1, mode_error exception 14.4, open file 14.1, positive_count 14.3, status_error exception 14.4, use_error exception 14.4 > 14.2.5 Specification of the Package Direct_IO with IO_EXCEPTIONS; generic type ELEMENT_TYPE is private; package DIRECT_IO is type FILE_TYPE is limited private; type FILE_MODE is (IN_FILE, INOUT_FILE, OUT_FILE); type COUNT is range 0 .. IMPLEMENTATION_DEFINED; subtype POSITIVE_COUNT is COUNT range 1 .. COUNT'LAST; -- File management procedure CREATE(FILE : in out FILE_TYPE; MODE : in FILE_MODE := INOUT_FILE; NAME : in STRING := ""; FORM : in STRING := ""); procedure OPEN (FILE : in out FILE_TYPE; MODE : in FILE_MODE; NAME : in STRING; FORM : in STRING := ""); procedure CLOSE (FILE : in out FILE_TYPE); procedure DELETE(FILE : in out FILE_TYPE); procedure RESET (FILE : in out FILE_TYPE; MODE : in FILE_MODE); procedure RESET (FILE : in out FILE_TYPE); function MODE (FILE : in FILE_TYPE) return FILE_MODE; function NAME (FILE : in FILE_TYPE) return STRING; function FORM (FILE : in FILE_TYPE) return STRING; function IS_OPEN(FILE : in FILE_TYPE) return BOOLEAN; -- Input and output operations procedure READ (FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE; FROM : POSITIVE_COUNT); procedure READ (FILE : in FILE_TYPE; ITEM : out ELEMENT_TYPE); procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE; TO : POSITIVE_COUNT); procedure WRITE(FILE : in FILE_TYPE; ITEM : in ELEMENT_TYPE); procedure SET_INDEX(FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); function INDEX(FILE : in FILE_TYPE) return POSITIVE_COUNT; function SIZE (FILE : in FILE_TYPE) return COUNT; function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; -- Exceptions STATUS_ERROR : exception renames IO_EXCEPTIONS.STATUS_ERROR; MODE_ERROR : exception renames IO_EXCEPTIONS.MODE_ERROR; NAME_ERROR : exception renames IO_EXCEPTIONS.NAME_ERROR; USE_ERROR : exception renames IO_EXCEPTIONS.USE_ERROR; DEVICE_ERROR : exception renames IO_EXCEPTIONS.DEVICE_ERROR; END_ERROR : exception renames IO_EXCEPTIONS.END_ERROR; DATA_ERROR : exception renames IO_EXCEPTIONS.DATA_ERROR; private -- implementation-dependent end DIRECT_IO; References close procedure 14.2.1, count type 14.2, create procedure 14.2.1, data_error exception 14.4, default_mode 14.2.5, delete procedure 14.2.1, device_error exception 14.4, element_type 14.2.4, end_error exception 14.4, end_of_file function 14.2.4, file_mode 14.2.5, file_type 14.2.4, form function 14.2.1, in_file 14.2.4, index function 14.2.4, inout_file 14.2.4 14.2.1, io_exceptions package 14.4, is_open function 14.2.1, mode function 14.2.1, mode_error exception 14.4, name function 14.2.1, name_error exception 14.4, open procedure 14.2.1, out_file 14.2.1, read procedure 14.2.4, set_index procedure 14.2.4, size function 14.2.4, status_error exception 14.4, use_error exception 14.4, write procedure 14.2.4 14.2.1 > 14.3 Text Input-Output This section describes the package TEXT_IO, which provides facilities for input and output in human-readable form. Each file is read or written sequentially, as a sequence of characters grouped into lines, and as a sequence of lines grouped into pages. The specification of the package is given below in section 14.3.10. The facilities for file management given above, in sections 14.2.1 and 14.2.2, are available for text input-output. In place of READ and WRITE, however, there are procedures GET and PUT that input values of suitable types from text files, and output values to them. These values are provided to the PUT procedures, and returned by the GET procedures, in a parameter ITEM. Several overloaded procedures of these names exist, for different types of ITEM. These GET procedures analyze the input sequences of characters as lexical elements (see Chapter 2) and return the corresponding values; the PUT procedures output the given values as appropriate lexical elements. Procedures GET and PUT are also available that input and output individual characters treated as character values rather than as lexical elements. In addition to the procedures GET and PUT for numeric and enumeration types of ITEM that operate on text files, analogous procedures are provided that read from and write to a parameter of type STRING. These procedures perform the same analysis and composition of character sequences as their counterparts which have a file parameter. For all GET and PUT procedures that operate on text files, and for many other subprograms, there are forms with and without a file parameter. Each such GET procedure operates on an input file, and each such PUT procedure operates on an output file. If no file is specified, a default input file or a default output file is used. At the beginning of program execution the default input and output files are the so-called standard input file and standard output file. These files are open, have respectively the current modes IN_FILE and OUT_FILE, and are associated with two implementation-defined external files. Procedures are provided to change the current default input file and the current default output file. From a logical point of view, a text file is a sequence of pages, a page is a sequence of lines, and a line is a sequence of characters; the end of a line is marked by a line terminator; the end of a page is marked by the combination of a line terminator immediately followed by a page terminator; and the end of a file is marked by the combination of a line terminator immediately followed by a page terminator and then a file terminator. Terminators are generated during output; either by calls of procedures provided expressly for that purpose; or implicitly as part of other operations, for example, when a bounded line length, a bounded page length, or both, have been specified for a file. The actual nature of terminators is not defined by the language and hence depends on the implementation. Although terminators are recognized or generated by certain of the procedures that follow, they are not necessarily implemented as characters or as sequences of characters. Whether they are characters (and if so which ones) in any particular implementation need not concern a user who neither explicitly outputs nor explicitly inputs control characters. The effect of input or output of control characters (other than horizontal tabulation) is not defined by the language. The characters of a line are numbered, starting from one; the number of a character is called its column number. For a line terminator, a column number is also defined: it is one more than the number of characters in the line. The lines of a page, and the pages of a file, are similarly numbered. The current column number is the column number of the next character or line terminator to be transferred. The current line number is the number of the current line. The current page number is the number of the current page. These numbers are values of the subtype POSITIVE_COUNT of the type COUNT (by convention, the value zero of the type COUNT is used to indicate special conditions). type COUNT is range 0 .. implementation_defined; subtype POSITIVE_COUNT is COUNT range 1 .. COUNT'LAST; For an output file, a maximum line length can be specified and a maximum page length can be specified. If a value to be output cannot fit on the current line, for a specified maximum line length, then a new line is automatically started before the value is output; if, further, this new line cannot fit on the current page, for a specified maximum page length, then a new page is automatically started before the value is output. Functions are provided to determine the maximum line length and the maximum page length. When a file is opened with mode OUT_FILE, both values are zero: by convention, this means that the line lengths and page lengths are unbounded. (Consequently, output consists of a single line if the subprograms for explicit control of line and page structure are not used.) The constant UNBOUNDED is provided for this purpose. References: count type 14.3.10, default current input file 14.3.2, default current output file 14.3.2, external file 14.1, file 14.1, get procedure 14.3.5, in_file 14.1, out_file 14.1, put procedure 14.3.5, read 14.2.2, sequential access 14.1, standard input file 14.3.2, standard output file 14.3.2 > 14.3.1 File Management The only allowed file modes for text files are the modes IN_FILE and OUT_FILE. The subprograms given in section 14.2.1 for the control of external files, and the function END_OF_FILE given in section 14.2.2 for sequential input-output, are also available for text files. There is also a version of END_OF_FILE that refers to the current default input file. For text files, the procedures have the following additional effects: - For the procedures CREATE and OPEN: After opening a file with mode OUT_FILE, the page length and line length are unbounded (both have the conventional value zero). After opening a file with mode IN_FILE or OUT_FILE, the current column, current line, and current page numbers are set to one. - For the procedure CLOSE: If the file has the current mode OUT_FILE, has the effect of calling NEW_PAGE, unless the current page is already terminated; then outputs a file terminator. - For the procedure RESET: If the file has the current mode OUT_FILE, has the effect of calling NEW_PAGE, unless the current page is already terminated; then outputs a file terminator. If the new file mode is OUT_FILE, the page and line lengths are unbounded. For all modes, the current column, line, and page numbers are set to one. The exception MODE_ERROR is raised by the procedure RESET upon an attempt to change the mode of a file that is either the current default input file, or the current default output file. References: create procedure 14.2.1, current column number 14.3, current default input file 14.3, current line number 14.3, current page number 14.3, end_of_file 14.3, external file 14.1, file 14.1, file mode 14.1, file terminator 14.3, in_file 14.1, line length 14.3, mode_error exception 14.4, open procedure 14.2.1, out_file 14.1, page length 14.3, reset procedure 14.2.1 > 14.3.2 Default Input and Output Files The following subprograms provide for the control of the particular default files that are used when a file parameter is omitted from a GET, PUT or other operation of text input-output described below. procedure SET_INPUT(FILE : in FILE_TYPE); Operates on a file of mode IN_FILE. Sets the current default input file to FILE. The exception STATUS_ERROR is raised if the given file is not open. The exception MODE_ERROR is raised if the mode of the given file is not IN_FILE. procedure SET_OUTPUT(FILE : in FILE_TYPE); Operates on a file of mode OUT_FILE. Sets the current default output file to FILE. The exception STATUS_ERROR is raised if the given file is not open. The exception MODE_ERROR is raised if the mode of the given file is not OUT_FILE. function STANDARD_INPUT return FILE_TYPE; Returns the standard input file (see 14.3). function STANDARD_OUTPUT return FILE_TYPE; Returns the standard output file (see 14.3). function CURRENT_INPUT return FILE_TYPE; Returns the current default input file. function CURRENT_OUTPUT return FILE_TYPE; Returns the current default output file. Note: The standard input and the standard output files cannot be opened, closed, reset, or deleted, because the parameter FILE of the corresponding procedures has the mode in out. References: current default file 14.3, default file 14.3, file_type 14.1, get procedure 14.3.5, mode_error exception 14.4, put procedure 14.3.5, status_error exception 14.4 > 14.3.3 Specification of Line and Page Lengths The subprograms described in this section are concerned with the line and page structure of a file of mode OUT_FILE. They operate either on the file given as the first parameter, or, in the absence of such a file parameter, on the current default output file. They provide for output of text with a specified maximum line length or page length. In these cases, line and page terminators are output implicitly and automatically when needed. When line and page lengths are unbounded (that is, when they have the conventional value zero), as in the case of a newly opened file, new lines and new pages are only started when explicitly called for. In all cases, the exception STATUS_ERROR is raised if the file to be used is not open; the exception MODE_ERROR is raised if the mode of the file is not OUT_FILE. procedure SET_LINE_LENGTH(FILE : in FILE_TYPE; TO : in COUNT); procedure SET_LINE_LENGTH(TO : in COUNT); Sets the maximum line length of the specified output file to the number of characters specified by TO. The value zero for TO specifies an unbounded line length. The exception USE_ERROR is raised if the specified line length is inappropriate for the associated external file. procedure SET_PAGE_LENGTH(FILE : in FILE_TYPE; TO : in COUNT); procedure SET_PAGE_LENGTH(TO : in COUNT); Sets the maximum page length of the specified output file to the number of lines specified by TO. The value zero for TO specifies an unbounded page length. The exception USE_ERROR is raised if the specified page length is inappropriate for the associated external file. function LINE_LENGTH(FILE : in FILE_TYPE) return COUNT; function LINE_LENGTH return COUNT; Returns the maximum line length currently set for the specified output file, or zero if the line length is unbounded. function PAGE_LENGTH(FILE : in FILE_TYPE) return COUNT; function PAGE_LENGTH return COUNT; Returns the maximum page length currently set for the specified output file, or zero if the page length is unbounded. References: count type 14.3, current default output file 14.3, external file 14.1, file 14.1, file_type 14.1, line 14.3, line length 14.3, line terminator 14.3, maximum line length 14.3, maximum page length 14.3, mode_error exception 14.4, open file 14.1, out_file 14.1, page 14.3, page length 14.3, page terminator 14.3, status_error exception 14.4, unbounded page length 14.3, use_error exception 14.4 > 14.3.4 Operations on Columns, Lines, and Pages The subprograms described in this section provide for explicit control of line and page structure; they operate either on the file given as the first parameter, or, in the absence of such a file parameter, on the appropriate (input or output) current default file. The exception STATUS_ERROR is raised by any of these subprograms if the file to be used is not open. procedure NEW_LINE(FILE : in FILE_TYPE; SPACING : in POSITIVE_COUNT := 1); procedure NEW_LINE(SPACING : in POSITIVE_COUNT := 1); Operates on a file of mode OUT_FILE. For a SPACING of one: Outputs a line terminator and sets the current column number to one. Then increments the current line number by one, except in the case that the current line number is already greater than or equal to the maximum page length, for a bounded page length; in that case a page terminator is output, the current page number is incremented by one, and the current line number is set to one. For a SPACING greater than one, the above actions are performed SPACING times. The exception MODE_ERROR is raised if the mode is not OUT_FILE. procedure SKIP_LINE(FILE : in FILE_TYPE; SPACING : in POSITIVE_COUNT := 1); procedure SKIP_LINE(SPACING : in POSITIVE_COUNT := 1); Operates on a file of mode IN_FILE. For a SPACING of one: Reads and discards all characters until a line terminator has been read, and then sets the current column number to one. If the line terminator is not immediately followed by a page terminator, the current line number is incremented by one. Otherwise, if the line terminator is immediately followed by a page terminator, then the page terminator is skipped, the current page number is incremented by one, and the current line number is set to one. For a SPACING greater than one, the above actions are performed SPACING times. The exception MODE_ERROR is raised if the mode is not IN_FILE. The exception END_ERROR is raised if an attempt is made to read a file terminator. function END_OF_LINE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_LINE return BOOLEAN; Operates on a file of mode IN_FILE. Returns TRUE if a line terminator or a file terminator is next; otherwise returns FALSE. The exception MODE_ERROR is raised if the mode is not IN_FILE. procedure NEW_PAGE(FILE : in FILE_TYPE); procedure NEW_PAGE; Operates on a file of mode OUT_FILE. Outputs a line terminator if the current line is not terminated, or if the current page is empty (that is, if the current column and line numbers are both equal to one). Then outputs a page terminator, which terminates the current page. Adds one to the current page number and sets the current column and line numbers to one. The exception MODE_ERROR is raised if the mode is not OUT_FILE. procedure SKIP_PAGE(FILE: in FILE_TYPE); procedure SKIP_PAGE; Operates on a file of mode IN_FILE. Reads and discards all characters and line terminators until a page terminator has been read. Then adds one to the current page number, and sets the current column and line numbers to one. The exception MODE_ERROR is raised if the mode is not IN_FILE. The exception END_ERROR is raised if an attempt is made to read a file terminator. function END_OF_PAGE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_PAGE return BOOLEAN; Operates on a file of mode IN_FILE. Returns TRUE if the combination of a line terminator and a page terminator is next, or if a file terminator is next; otherwise returns FALSE. The exception MODE_ERROR is raised if the mode is not IN_FILE. function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_FILE return BOOLEAN; Operates on a file of mode IN_FILE. Returns TRUE if a file terminator is next, or if the combination of a line, a page, and a file terminator is next; otherwise returns FALSE. The exception MODE_ERROR is raised if the mode is not IN_FILE. The following subprograms provide for the control of the current position of reading or writing in a file. In all cases, the default file is the current output file. procedure SET_COL(FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); procedure SET_COL(TO : in POSITIVE_COUNT); If the file mode is OUT_FILE: If the value specified by TO is greater than the current column number, outputs spaces, adding one to the current column number after each space, until the current column number equals the specified value. If the value specified by TO is equal to the current column number, there is no effect. If the value specified by TO is less than the current column number, has the effect of calling NEW_LINE (with a spacing of one), then outputs (TO - 1) spaces, and sets the current column number to the specified value. The exception LAYOUT_ERROR is raised if the value specified by TO exceeds LINE_LENGTH when the line length is bounded (that is, when it does not have the conventional value zero). If the file mode is IN_FILE: Reads (and discards) individual characters, line terminators, and page terminators, until the next character to be read has a column number that equals the value specified by TO; there is no effect if the current column number already equals this value. Each transfer of a character or terminator maintains the current column, line, and page numbers in the same way as a GET procedure (see 14.3.5). (Short lines will be skipped until a line is reached that has a character at the specified column position.) The exception END_ERROR is raised if an attempt is made to read a file terminator. procedure SET_LINE(FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); procedure SET_LINE(TO : in POSITIVE_COUNT); If the file mode is OUT_FILE: If the value specified by TO is greater than the current line number, has the effect of repeatedly calling NEW_LINE (with a spacing of one), until the current line number equals the specified value. If the value specified by TO is equal to the current line number, there is no effect. If the value specified by TO is less than the current line number, has the effect of calling NEW_PAGE followed by a call of NEW_LINE with a spacing equal to (TO - 1). The exception LAYOUT_ERROR is raised if the value specified by TO exceeds PAGE_LENGTH when the page length is bounded (that is, when it does not have the conventional value zero). If the mode is IN_FILE: Has the effect of repeatedly calling SKIP_LINE (with a spacing of one), until the current line number equals the value specified by TO; there is no effect if the current line number already equals this value. (Short pages will be skipped until a page is reached that has a line at the specified line position.) The exception END_ERROR is raised if an attempt is made to read a file terminator. function COL(FILE : in FILE_TYPE) return POSITIVE_COUNT; function COL return POSITIVE_COUNT; Returns the current column number. The exception LAYOUT_ERROR is raised if this number exceeds COUNT'LAST. function LINE(FILE : in FILE_TYPE) return POSITIVE_COUNT; function LINE return POSITIVE_COUNT; Returns the current line number. The exception LAYOUT_ERROR is raised if this number exceeds COUNT'LAST. function PAGE(FILE : in FILE_TYPE) return POSITIVE_COUNT; function PAGE return POSITIVE_COUNT; Returns the current page number. The exception LAYOUT_ERROR is raised if this number exceeds COUNT'LAST. The column number, line number, or page number are allowed to exceed COUNT'LAST (as a consequence of the input or output of sufficiently many characters, lines, or pages). These events do not cause any exception to be raised. However, a call of COL, LINE, or PAGE raises the exception LAYOUT_ERROR if the corresponding number exceeds COUNT'LAST. Note: A page terminator is always skipped whenever the preceding line terminator is skipped. An implementation may represent the combination of these terminators by a single character, provided that it is properly recognized at input. References: current column number 14.3, current default file 14.3, current line number 14.3, current page number 14.3, end_error exception 14.4, file 14.1, file terminator 14.3, get procedure 14.3.5, in_file 14.1, layout_error exception 14.4, line 14.3, line number 14.3, line terminator 14.3, maximum page length 14.3, mode_error exception 14.4, open file 14.1, page 14.3, page length 14.3, page terminator 14.3, positive count 14.3, status_error exception 14.4 > 14.3.5 Get and Put Procedures The procedures GET and PUT for items of the types CHARACTER, STRING, numeric types, and enumeration types are described in subsequent sections. Features of these procedures that are common to most of these types are described in this section. The GET and PUT procedures for items of type CHARACTER and STRING deal with individual character values; the GET and PUT procedures for numeric and enumeration types treat the items as lexical elements. All procedures GET and PUT have forms with a file parameter, written first. Where this parameter is omitted, the appropriate (input or output) current default file is understood to be specified. Each procedure GET operates on a file of mode IN_FILE. Each procedure PUT operates on a file of mode OUT_FILE. All procedures GET and PUT maintain the current column, line, and page numbers of the specified file: the effect of each of these procedures upon these numbers is the resultant of the effects of individual transfers of characters and of individual output or skipping of terminators. Each transfer of a character adds one to the current column number. Each output of a line terminator sets the current column number to one and adds one to the current line number. Each output of a page terminator sets the current column and line numbers to one and adds one to the current page number. For input, each skipping of a line terminator sets the current column number to one and adds one to the current line number; each skipping of a page terminator sets the current column and line numbers to one and adds one to the current page number. Similar considerations apply to the procedures GET_LINE, PUT_LINE, and SET_COL. Several GET and PUT procedures, for numeric and enumeration types, have format parameters which specify field lengths; these parameters are of the nonnegative subtype FIELD of the type INTEGER. Input-output of enumeration values uses the syntax of the corresponding lexical elements. Any GET procedure for an enumeration type begins by skipping any leading blanks, or line or page terminators; a blank being defined as a space or a horizontal tabulation character. Next, characters are input only so long as the sequence input is an initial sequence of an identifier or of a character literal (in particular, input ceases when a line terminator is encountered). The character or line terminator that causes input to cease remains available for subsequent input. For a numeric type, the GET procedures have a format parameter called WIDTH. If the value given for this parameter is zero, the GET procedure proceeds in the same manner as for enumeration types, but using the syntax of numeric literals instead of that of enumeration literals. If a nonzero value is given, then exactly WIDTH characters are input, or the characters up to a line terminator, whichever comes first; any skipped leading blanks are included in the count. The syntax used for numeric literals is an extended syntax that allows a leading sign (but no intervening blanks, or line or page terminators). Any PUT procedure, for an item of a numeric or an enumeration type, outputs the value of the item as a numeric literal, identifier, or character literal, as appropriate. This is preceded by leading spaces if required by the format parameters WIDTH or FORE (as described in later sections), and then a minus sign for a negative value; for an enumeration type, the spaces follow instead of leading. The format given for a PUT procedure is overridden if it is insufficiently wide. Two further cases arise for PUT procedures for numeric and enumeration types, if the line length of the specified output file is bounded (that is, if it does not have the conventional value zero). If the number of characters to be output does not exceed the maximum line length, but is such that they cannot fit on the current line, starting from the current column, then (in effect) NEW_LINE is called (with a spacing of one) before output of the item. Otherwise, if the number of characters exceeds the maximum line length, then the exception LAYOUT_ERROR is raised and no characters are output. The exception STATUS_ERROR is raised by any of the procedures GET, GET_LINE, PUT, and PUT_LINE if the file to be used is not open. The exception MODE_ERROR is raised by the procedures GET and GET_LINE if the mode of the file to be used is not IN_FILE; and by the procedures PUT and PUT_LINE, if the mode is not OUT_FILE. The exception END_ERROR is raised by a GET procedure if an attempt is made to skip a file terminator. The exception DATA_ERROR is raised by a GET procedure if the sequence finally input is not a lexical element corresponding to the type, in particular if no characters were input; for this test, leading blanks are ignored; for an item of a numeric type, when a sign is input, this rule applies to the succeeding numeric literal. The exception LAYOUT_ERROR is raised by a PUT procedure that outputs to a parameter of type STRING, if the length of the actual string is insufficient for the output of the item. Examples: In the examples, here and in sections 14.3.7 and 14.3.8, the string quotes and the lower case letter b are not transferred: they are shown only to reveal the layout and spaces. N : INTEGER; ... GET(N); -- Characters at input Sequence input Value of N -- bb-12535b -12535 -12535 -- bb12_535E1b 12_535E1 125350 -- bb12_535E; 12_535E (none) DATA_ERROR raised Example of overridden width parameter: PUT(ITEM => -23, WIDTH => 2); -- "-23" References: blank 14.3.9, column number 14.3, current default file 14.3, data_error exception 14.4, end_error exception 14.4, file 14.1, fore 14.3.8, get procedure 14.3.6 14.3.7 14.3.8 14.3.9, in_file 14.1, layout_error exception 14.4, line number 14.1, line terminator 14.1, maximum line length 14.3, mode 14.1, mode_error exception 14.4, new_file procedure 14.3.4, out_file 14.1, page number 14.1, page terminator 14.1, put procedure 14.3.6 14.3.7 14.3.8 14.3.9, skipping 14.3.7 14.3.8 14.3.9, status_error exception 14.4, width 14.3.5 14.3.7 14.3.9 > 14.3.6 Input-Output of Characters and Strings For an item of type CHARACTER the following procedures are provided: procedure GET(FILE : in FILE_TYPE; ITEM : out CHARACTER); procedure GET(ITEM : out CHARACTER); After skipping any line terminators and any page terminators, reads the next character from the specified input file and returns the value of this character in the out parameter ITEM. The exception END_ERROR is raised if an attempt is made to skip a file terminator. procedure PUT(FILE : in FILE_TYPE; ITEM : in CHARACTER); procedure PUT(ITEM : in CHARACTER); If the line length of the specified output file is bounded (that is, does not have the conventional value zero), and the current column number exceeds it, has the effect of calling NEW_LINE with a spacing of one. Then, or otherwise, outputs the given character to the file. For an item of type STRING the following procedures are provided: procedure GET(FILE : in FILE_TYPE; ITEM : out STRING); procedure GET(ITEM : out STRING); Determines the length of the given string and attempts that number of GET operations for successive characters of the string (in particular, no operation is performed if the string is null). procedure PUT(FILE : in FILE_TYPE; ITEM : in STRING); procedure PUT(ITEM : in STRING); Determines the length of the given string and attempts that number of PUT operations for successive characters of the string (in particular, no operation is performed if the string is null). procedure GET_LINE(FILE : in FILE_TYPE; ITEM : out STRING; LAST : out NATURAL); procedure GET_LINE(ITEM : out STRING; LAST : out NATURAL); Replaces successive characters of the specified string by successive characters read from the specified input file. Reading stops if the end of the line is met, in which case the procedure SKIP_LINE is then called (in effect) with a spacing of one; reading also stops if the end of the string is met. Characters not replaced are left undefined. If characters are read, returns in LAST the index value such that ITEM(LAST) is the last character replaced (the index of the first character replaced is ITEM'FIRST). If no characters are read, returns in LAST an index value that is one less than ITEM'FIRST. The exception END_ERROR is raised if an attempt is made to skip a file terminator. procedure PUT_LINE(FILE : in FILE_TYPE; ITEM : in STRING); procedure PUT_LINE(ITEM : in STRING); Calls the procedure PUT for the given string, and then the procedure NEW_LINE with a spacing of one. Notes: In a literal string parameter of PUT, the enclosing string bracket characters are not output. Each doubled string bracket character in the enclosed string is output as a single string bracket character, as a consequence of the rule for string literals (see 2.6). A string read by GET or written by PUT can extend over several lines. References: current column number 14.3, end_error exception 14.4, file 14.1, file terminator 14.3, get procedure 14.3.5, line 14.3, line length 14.3, new_line procedure 14.3.4, page terminator 14.3, put procedure 14.3.4, skipping 14.3.5 > 14.3.7 Input-Output for Integer Types The following procedures are defined in the generic package INTEGER_IO. This must be instantiated for the appropriate integer type (indicated by NUM in the specification). Values are output as decimal or based literals, without underline characters or exponent, and preceded by a minus sign if negative. The format (which includes any leading spaces and minus sign) can be specified by an optional field width parameter. Values of widths of fields in output formats are of the nonnegative integer subtype FIELD. Values of bases are of the integer subtype NUMBER_BASE. subtype NUMBER_BASE is INTEGER range 2 .. 16; The default field width and base to be used by output procedures are defined by the following variables that are declared in the generic package INTEGER_IO: DEFAULT_WIDTH : FIELD := NUM'WIDTH; DEFAULT_BASE : NUMBER_BASE := 10; The following procedures are provided: procedure GET(FILE : in FILE_TYPE; ITEM : out NUM; WIDTH : in FIELD := 0); procedure GET(ITEM : out NUM; WIDTH : in FIELD := 0); If the value of the parameter WIDTH is zero, skips any leading blanks, line terminators, or page terminators, then reads a plus or a minus sign if present, then reads according to the syntax of an integer literal (which may be a based literal). If a nonzero value of WIDTH is supplied, then exactly WIDTH characters are input, or the characters (possibly none) up to a line terminator, whichever comes first; any skipped leading blanks are included in the count. Returns, in the parameter ITEM, the value of type NUM that corresponds to the sequence input. The exception DATA_ERROR is raised if the sequence input does not have the required syntax or if the value obtained is not of the subtype NUM. procedure PUT(FILE : in FILE_TYPE; ITEM : in NUM; WIDTH : in FIELD := DEFAULT_WIDTH; BASE : in NUMBER_BASE := DEFAULT_BASE); procedure PUT(ITEM : in NUM; WIDTH : in FIELD := DEFAULT_WIDTH; BASE : in NUMBER_BASE := DEFAULT_BASE); Outputs the value of the parameter ITEM as an integer literal, with no underlines, no exponent, and no leading zeros (but a single zero for the value zero), and a preceding minus sign for a negative value. If the resulting sequence of characters to be output has fewer than WIDTH characters, then leading spaces are first output to make up the difference. Uses the syntax for decimal literal if the parameter BASE has the value ten (either explicitly or through DEFAULT_BASE); otherwise, uses the syntax for based literal, with any letters in upper case. procedure GET(FROM : in STRING; ITEM : out NUM; LAST : out POSITIVE); Reads an integer value from the beginning of the given string, following the same rules as the GET procedure that reads an integer value from a file, but treating the end of the string as a file terminator. Returns, in the parameter ITEM, the value of type NUM that corresponds to the sequence input. Returns in LAST the index value such that FROM(LAST) is the last character read. The exception DATA_ERROR is raised if the sequence input does not have the required syntax or if the value obtained is not of the subtype NUM. procedure PUT(TO : out STRING; ITEM : in NUM; BASE : in NUMBER_BASE := DEFAULT_BASE); Outputs the value of the parameter ITEM to the given string, following the same rule as for output to a file, using the length of the given string as the value for WIDTH. Examples: package INT_IO is new INTEGER_IO(SMALL_INT); use INT_IO; -- default format used at instantiation, DEFAULT_WIDTH = 4, DEFAULT_BASE = 10 PUT(126); -- "b126" PUT(-126, 7); -- "bbb-126" PUT(126, WIDTH => 13, BASE => 2); -- "bbb2#1111110#" References: based literal 2.4.2, blank 14.3.5, data_error exception 14.4, decimal literal 2.4.1, field subtype 14.3.5, file_type 14.1, get procedure 14.3.5, integer_io package 14.3.10, integer literal 2.4, layout_error exception 14.4, line terminator 14.3, put procedure 14.3.5, skipping 14.3.5, width 14.3.5 > 14.3.8 Input-Output for Real Types The following procedures are defined in the generic packages FLOAT_IO and FIXED_IO, which must be instantiated for the appropriate floating point or fixed point type respectively (indicated by NUM in the specifications). Values are output as decimal literals without underline characters. The format of each value output consists of a FORE field, a decimal point, an AFT field, and (if a nonzero EXP parameter is supplied) the letter E and an EXP field. The two possible formats thus correspond to: FORE . AFT and to: FORE . AFT E EXP without any spaces between these fields. The FORE field may include leading spaces, and a minus sign for negative values. The AFT field includes only decimal digits (possibly with trailing zeros). The EXP field includes the sign (plus or minus) and the exponent (possibly with leading zeros). For floating point types, the default lengths of these fields are defined by the following variables that are declared in the generic package FLOAT_IO: DEFAULT_FORE : FIELD := 2; DEFAULT_AFT : FIELD := NUM'DIGITS-1; DEFAULT_EXP : FIELD := 3; For fixed point types, the default lengths of these fields are defined by the following variables that are declared in the generic package FIXED_IO: DEFAULT_FORE : FIELD := NUM'FORE; DEFAULT_AFT : FIELD := NUM'AFT; DEFAULT_EXP : FIELD := 0; The following procedures are provided: procedure GET(FILE : in FILE_TYPE; ITEM : out NUM; WIDTH : in FIELD := 0); procedure GET(ITEM : out NUM; WIDTH : in FIELD := 0); If the value of the parameter WIDTH is zero, skips any leading blanks, line terminators, or page terminators, then reads a plus or a minus sign if present, then reads according to the syntax of a real literal (which may be a based literal). If a nonzero value of WIDTH is supplied, then exactly WIDTH characters are input, or the characters (possibly none) up to a line terminator, whichever comes first; any skipped leading blanks are included in the count. Returns, in the parameter ITEM, the value of type NUM that corresponds to the sequence input. The exception DATA_ERROR is raised if the sequence input does not have the required syntax or if the value obtained is not of the subtype NUM. procedure PUT(FILE : in FILE_TYPE; ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); procedure PUT(ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); Outputs the value of the parameter ITEM as a decimal literal with the format defined by FORE, AFT and EXP. If the value is negative, a minus sign is included in the integer part. If EXP has the value zero, then the integer part to be output has as many digits as are needed to represent the integer part of the value of ITEM, overriding FORE if necessary, or consists of the digit zero if the value of ITEM has no integer part. If EXP has a value greater than zero, then the integer part to be output has a single digit, which is nonzero except for the value 0.0 of ITEM. In both cases, however, if the integer part to be output has fewer than FORE characters, including any minus sign, then leading spaces are first output to make up the difference. The number of digits of the fractional part is given by AFT, or is one if AFT equals zero. The value is rounded; a value of exactly one half in the last place may be rounded either up or down. If EXP has the value zero, there is no exponent part. If EXP has a value greater than zero, then the exponent part to be output has as many digits as are needed to represent the exponent part of the value of ITEM (for which a single digit integer part is used), and includes an initial sign (plus or minus). If the exponent part to be output has fewer than EXP characters, including the sign, then leading zeros precede the digits, to make up the difference. For the value 0.0 of ITEM, the exponent has the value zero. procedure GET(FROM : in STRING; ITEM : out NUM; LAST : out POSITIVE); Reads a real value from the beginning of the given string, following the same rule as the GET procedure that reads a real value from a file, but treating the end of the string as a file terminator. Returns, in the parameter ITEM, the value of type NUM that corresponds to the sequence input. Returns in LAST the index value such that FROM(LAST) is the last character read. The exception DATA_ERROR is raised if the sequence input does not have the required syntax, or if the value obtained is not of the subtype NUM. procedure PUT(TO : out STRING; ITEM : in NUM; AFT : in FIELD := DEFAULT_AFT; EXP : in INTEGER := DEFAULT_EXP); Outputs the value of the parameter ITEM to the given string, following the same rule as for output to a file, using a value for FORE such that the sequence of characters output exactly fills the string, including any leading spaces. Examples: package REAL_IO is new FLOAT_IO(REAL); use REAL_IO; -- default format used at instantiation, DEFAULT_EXP = 3 X : REAL := -123.4567; -- digits 8 (see 3.5.7) PUT(X); -- default format "-1.2345670E+02" PUT(X, FORE => 5, AFT => 3, EXP => 2); -- "bbb-1.235E+2" PUT(X, 5, 3, 0); -- "b-123.457" Note: For an item with a positive value, if output to a string exactly fills the string without leading spaces, then output of the corresponding negative value will raise LAYOUT_ERROR. References: aft attribute 3.5.10, based literal 2.4.2, blank 14.3.5, data_error exception 14.3.5, decimal literal 2.4.1, field subtype 14.3.5, file_type 14.1, fixed_io package 14.3.10, floating_io package 14.3.10, fore attribute 3.5.10, get procedure 14.3.5, layout_error 14.3.5, line terminator 14.3.5, put procedure 14.3.5, real literal 2.4, skipping 14.3.5, width 14.3.5 > 14.3.9 Input-Output for Enumeration Types The following procedures are defined in the generic package ENUMERATION_IO, which must be instantiated for the appropriate enumeration type (indicated by ENUM in the specification). Values are output using either upper or lower case letters for identifiers. This is specified by the parameter SET, which is of the enumeration type TYPE_SET. type TYPE_SET is (LOWER_CASE, UPPER_CASE); The format (which includes any trailing spaces) can be specified by an optional field width parameter. The default field width and letter case are defined by the following variables that are declared in the generic package ENUMERATION_IO: DEFAULT_WIDTH : FIELD := 0; DEFAULT_SETTING : TYPE_SET := UPPER_CASE; The following procedures are provided: procedure GET(FILE : in FILE_TYPE; ITEM : out ENUM); procedure GET(ITEM : out ENUM); After skipping any leading blanks, line terminators, or page terminators, reads an identifier according to the syntax of this lexical element (lower and upper case being considered equivalent), or a character literal according to the syntax of this lexical element (including the apostrophes). Returns, in the parameter ITEM, the value of type ENUM that corresponds to the sequence input. The exception DATA_ERROR is raised if the sequence input does not have the required syntax, or if the identifier or character literal does not correspond to a value of the subtype ENUM. procedure PUT(FILE : in FILE_TYPE; ITEM : in ENUM; WIDTH : in FIELD := DEFAULT_WIDTH; SET : in TYPE_SET := DEFAULT_SETTING); procedure PUT(ITEM : in ENUM; WIDTH : in FIELD := DEFAULT_WIDTH; SET : in TYPE_SET := DEFAULT_SETTING); Outputs the value of the parameter ITEM as an enumeration literal (either an identifier or a character literal). The optional parameter SET indicates whether lower case or upper case is used for identifiers; it has no effect for character literals. If the sequence of characters produced has fewer than WIDTH characters, then trailing spaces are finally output to make up the difference. procedure GET(FROM : in STRING; ITEM : out ENUM; LAST : out POSITIVE); Reads an enumeration value from the beginning of the given string, following the same rule as the GET procedure that reads an enumeration value from a file, but treating the end of the string as a file terminator. Returns, in the parameter ITEM, the value of type ENUM that corresponds to the sequence input. Returns in LAST the index value such that FROM(LAST) is the last character read. The exception DATA_ERROR is raised if the sequence input does not have the required syntax, or if the identifier or character literal does not correspond to a value of the subtype ENUM. procedure PUT(TO : out STRING; ITEM : in ENUM; SET : in TYPE_SET := DEFAULT_SETTING); Outputs the value of the parameter ITEM to the given string, following the same rule as for output to a file, using the length of the given string as the value for WIDTH. Although the specification of the package ENUMERATION_IO would allow instantiation for an integer type, this is not the intended purpose of this generic package, and the effect of such instantiations is not defined by the language. Notes: There is a difference between PUT defined for characters, and for enumeration values. Thus TEXT_IO.PUT('A'); -- outputs the character A package CHAR_IO is new TEXT_IO.ENUMERATION_IO(CHARACTER); CHAR_IO.PUT('A'); -- outputs the character 'A', between single quotes The type BOOLEAN is an enumeration type, hence ENUMERATION_IO can be instantiated for this type. References: blank 14.3.5, data_error 14.3.5, enumeration_io package 14.3.10, field subtype 14.3.5, file_type 14.1, get procedure 14.3.5, line terminator 14.3.5, put procedure 14.3.5, skipping 14.3.5, width 14.3.5 > 14.3.10 Specification of the Package Text_IO with IO_EXCEPTIONS; package TEXT_IO is type FILE_TYPE is limited private; type FILE_MODE is (IN_FILE, OUT_FILE); type COUNT is range 0 .. IMPLEMENTATION_DEFINED; subtype POSITIVE_COUNT is COUNT range 1 .. COUNT'LAST; UNBOUNDED : constant COUNT := 0; -- line and page length subtype FIELD is INTEGER range 0 .. IMPLEMENTATION_DEFINED; subtype NUMBER_BASE is INTEGER range 2 .. 16; type TYPE_SET is (LOWER_CASE, UPPER_CASE); -- File Management procedure CREATE (FILE : in out FILE_TYPE; MODE : in FILE_MODE := OUT_FILE; NAME : in STRING := ""; FORM : in STRING := ""); procedure OPEN (FILE : in out FILE_TYPE; MODE : in FILE_MODE; NAME : in STRING; FORM : in STRING := ""); procedure CLOSE (FILE : in out FILE_TYPE); procedure DELETE (FILE : in out FILE_TYPE); procedure RESET (FILE : in out FILE_TYPE; MODE : in FILE_MODE); procedure RESET (FILE : in out FILE_TYPE); function MODE (FILE : in FILE_TYPE) return FILE_MODE; function NAME (FILE : in FILE_TYPE) return STRING; function FORM (FILE : in FILE_TYPE) return STRING; function IS_OPEN(FILE : in FILE_TYPE) return BOOLEAN; -- Control of default input and output files procedure SET_INPUT (FILE : in FILE_TYPE); procedure SET_OUTPUT(FILE : in FILE_TYPE); function STANDARD_INPUT return FILE_TYPE; function STANDARD_OUTPUT return FILE_TYPE; function CURRENT_INPUT return FILE_TYPE; function CURRENT_OUTPUT return FILE_TYPE; -- Specification of line and page lengths procedure SET_LINE_LENGTH(FILE : in FILE_TYPE; TO : in COUNT); procedure SET_LINE_LENGTH(TO : in COUNT); procedure SET_PAGE_LENGTH(FILE : in FILE_TYPE; TO : in COUNT); procedure SET_PAGE_LENGTH(TO : in COUNT); function LINE_LENGTH(FILE : in FILE_TYPE) return COUNT; function LINE_LENGTH return COUNT; function PAGE_LENGTH(FILE : in FILE_TYPE) return COUNT; function PAGE_LENGTH return COUNT; -- Column, Line, and Page Control procedure NEW_LINE (FILE : in FILE_TYPE; SPACING : in POSITIVE_COUNT := 1); procedure NEW_LINE (SPACING : in POSITIVE_COUNT := 1); procedure SKIP_LINE (FILE : in FILE_TYPE; SPACING : in POSITIVE_COUNT := 1); procedure SKIP_LINE (SPACING : in POSITIVE_COUNT := 1); function END_OF_LINE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_LINE return BOOLEAN; procedure NEW_PAGE (FILE : in FILE_TYPE); procedure NEW_PAGE; procedure SKIP_PAGE (FILE : in FILE_TYPE); procedure SKIP_PAGE; function END_OF_PAGE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_PAGE return BOOLEAN; function END_OF_FILE(FILE : in FILE_TYPE) return BOOLEAN; function END_OF_FILE return BOOLEAN; procedure SET_COL (FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); procedure SET_COL (TO : in POSITIVE_COUNT); procedure SET_LINE(FILE : in FILE_TYPE; TO : in POSITIVE_COUNT); procedure SET_LINE(TO : in POSITIVE_COUNT); function COL (FILE : in FILE_TYPE) return POSITIVE_COUNT; function COL return POSITIVE_COUNT; function LINE(FILE : in FILE_TYPE) return POSITIVE_COUNT; function LINE return POSITIVE_COUNT; function PAGE(FILE : in FILE_TYPE) return POSITIVE_COUNT; function PAGE return POSITIVE_COUNT; -- Character Input-Output procedure GET(FILE : in FILE_TYPE; ITEM : out CHARACTER); procedure GET(ITEM : out CHARACTER); procedure PUT(FILE : in FILE_TYPE; ITEM : in CHARACTER); procedure PUT(ITEM : in CHARACTER); -- String Input-Output procedure GET(FILE : in FILE_TYPE; ITEM : out STRING); procedure GET(ITEM : out STRING); procedure PUT(FILE : in FILE_TYPE; ITEM : in STRING); procedure PUT(ITEM : in STRING); procedure GET_LINE(FILE : in FILE_TYPE; ITEM : out STRING; LAST : out NATURAL); procedure GET_LINE(ITEM : out STRING; LAST : out NATURAL); procedure PUT_LINE(FILE : in FILE_TYPE; ITEM : in STRING); procedure PUT_LINE(ITEM : in STRING); -- Generic package for Input-Output of Integer Types generic type NUM is range <>; package INTEGER_IO is DEFAULT_WIDTH : FIELD := NUM'WIDTH; DEFAULT_BASE : NUMBER_BASE := 10; procedure GET(FILE : in FILE_TYPE; ITEM : out NUM; WIDTH : in FIELD := 0); procedure GET(ITEM : out NUM; WIDTH : in FIELD := 0); procedure PUT(FILE : in FILE_TYPE; ITEM : in NUM; WIDTH : in FIELD := DEFAULT_WIDTH; BASE : in NUMBER_BASE := DEFAULT_BASE); procedure PUT(ITEM : in NUM; WIDTH : in FIELD := DEFAULT_WIDTH; BASE : in NUMBER_BASE := DEFAULT_BASE); procedure GET(FROM : in STRING; ITEM : out NUM; LAST : out POSITIVE); procedure PUT(TO : out STRING; ITEM : in NUM; BASE : in NUMBER_BASE := DEFAULT_BASE); end INTEGER_IO; -- Generic packages for Input-Output of Real Types generic type NUM is digits <>; package FLOAT_IO is DEFAULT_FORE : FIELD := 2; DEFAULT_AFT : FIELD := NUM'DIGITS-1; DEFAULT_EXP : FIELD := 3; procedure GET(FILE : in FILE_TYPE; ITEM : out NUM; WIDTH : in FIELD := 0); procedure GET(ITEM : out NUM; WIDTH : in FIELD := 0); procedure PUT(FILE : in FILE_TYPE; ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); procedure PUT(ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); procedure GET(FROM : in STRING; ITEM : out NUM; LAST : out POSITIVE); procedure PUT(TO : out STRING; ITEM : in NUM; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); end FLOAT_IO; generic type NUM is delta <>; package FIXED_IO is DEFAULT_FORE : FIELD := NUM'FORE; DEFAULT_AFT : FIELD := NUM'AFT; DEFAULT_EXP : FIELD := 0; procedure GET(FILE : in FILE_TYPE; ITEM : out NUM; WIDTH : in FIELD := 0); procedure GET(ITEM : out NUM; WIDTH : in FIELD := 0); procedure PUT(FILE : in FILE_TYPE; ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); procedure PUT(ITEM : in NUM; FORE : in FIELD := DEFAULT_FORE; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); procedure GET(FROM : in STRING; ITEM : out NUM; LAST : out POSITIVE); procedure PUT(TO : out STRING; ITEM : in NUM; AFT : in FIELD := DEFAULT_AFT; EXP : in FIELD := DEFAULT_EXP); end FIXED_IO; -- Generic package for Input-Output of Enumeration Types generic type ENUM is (<>); package ENUMERATION_IO is DEFAULT_WIDTH : FIELD := 0; DEFAULT_SETTING : TYPE_SET := UPPER_CASE; procedure GET(FILE : in FILE_TYPE; ITEM : out ENUM); procedure GET(ITEM : out ENUM); procedure PUT(FILE : in FILE_TYPE; ITEM : in ENUM; WIDTH : in FIELD := DEFAULT_WIDTH; SET : in TYPE_SET := DEFAULT_SETTING); procedure PUT(ITEM : in ENUM; WIDTH : in FIELD := DEFAULT_WIDTH; SET : in TYPE_SET := DEFAULT_SETTING); procedure GET(FROM : in STRING; ITEM : out ENUM; LAST : out POSITIVE); procedure PUT(TO : out STRING; ITEM : in ENUM; SET : in TYPE_SET := DEFAULT_SETTING); end ENUMERATION_IO; -- Exceptions STATUS_ERROR : exception renames IO_EXCEPTIONS.STATUS_ERROR; MODE_ERROR : exception renames IO_EXCEPTIONS.MODE_ERROR; NAME_ERROR : exception renames IO_EXCEPTIONS.NAME_ERROR; USE_ERROR : exception renames IO_EXCEPTIONS.USE_ERROR; DEVICE_ERROR : exception renames IO_EXCEPTIONS.DEVICE_ERROR; END_ERROR : exception renames IO_EXCEPTIONS.END_ERROR; DATA_ERROR : exception renames IO_EXCEPTIONS.DATA_ERROR; LAYOUT_ERROR : exception renames IO_EXCEPTIONS.LAYOUT_ERROR; private -- implementation-dependent end TEXT_IO; > 14.4 Exceptions in Input-Output The following exceptions can be raised by input-output operations. They are declared in the package IO_EXCEPTIONS, defined in section 14.5; this package is named in the context clause for each of the three input-output packages. Only outline descriptions are given of the conditions under which NAME_ERROR, USE_ERROR, and DEVICE_ERROR are raised; for full details see Appendix F. If more than one error condition exists, the corresponding exception that appears earliest in the following list is the one that is raised. The exception STATUS_ERROR is raised by an attempt to operate upon a file that is not open, and by an attempt to open a file that is already open. The exception MODE_ERROR is raised by an attempt to read from, or test for the end of, a file whose current mode is OUT_FILE, and also by an attempt to write to a file whose current mode is IN_FILE. In the case of TEXT_IO, the exception MODE_ERROR is also raised by specifying a file whose current mode is OUT_FILE in a call of SET_INPUT, SKIP_LINE, END_OF_LINE, SKIP_PAGE, or END_OF_PAGE; and by specifying a file whose current mode is IN_FILE in a call of SET_OUTPUT, SET_LINE_LENGTH, SET_PAGE_LENGTH, LINE_LENGTH, PAGE_LENGTH, NEW_LINE, or NEW_PAGE. The exception NAME_ERROR is raised by a call of CREATE or OPEN if the string given for the parameter NAME does not allow the identification of an external file. For example, this exception is raised if the string is improper, or, alternatively, if either none or more than one external file corresponds to the string. The exception USE_ERROR is raised if an operation is attempted that is not possible for reasons that depend on characteristics of the external file. For example, this exception is raised by the procedure CREATE, among other circumstances, if the given mode is OUT_FILE but the form specifies an input only device, if the parameter FORM specifies invalid access rights, or if an external file with the given name already exists and overwriting is not allowed. The exception DEVICE_ERROR is raised if an input-output operation cannot be completed because of a malfunction of the underlying system. The exception END_ERROR is raised by an attempt to skip (read past) the end of a file. The exception DATA_ERROR may be raised by the procedure READ if the element read cannot be interpreted as a value of the required type. This exception is also raised by a procedure GET (defined in the package TEXT_IO) if the input character sequence fails to satisfy the required syntax, or if the value input does not belong to the range of the required type or subtype. The exception LAYOUT_ERROR is raised (in text input-output) by COL, LINE, or PAGE if the value returned exceeds COUNT'LAST. The exception LAYOUT_ERROR is also raised on output by an attempt to set column or line numbers in excess of specified maximum line or page lengths, respectively (excluding the unbounded cases). It is also raised by an attempt to PUT too many characters to a string. References: col function 14.3.4, create procedure 14.2.1, end_of_line function 14.3.4, end_of_page function 14.3.4, external file 14.1, file 14.1, form string 14.1, get procedure 14.3.5, in_file 14.1, io_exceptions package 14.5, line function 14.3.4, line_length function 14.3.4, name string 14.1, new_line procedure 14.3.4, new_page procedure 14.3.4, open procedure 14.2.1, out_file 14.1, page function 14.3.4, page_length function 14.3.4, put procedure 14.3.5, read procedure 14.2.2 14.2.3, set_input procedure 14.3.2, set_line_length 14.3.3, set_page_length 14.3.3, set_output 14.3.2, skip_line procedure 14.3.4, skip_page procedure 14.3.4, text_io package 14.3 > 14.5 Specification of the Package IO_Exceptions This package defines the exceptions needed by the packages SEQUENTIAL_IO, DIRECT_IO, and TEXT_IO. package IO_EXCEPTIONS is STATUS_ERROR : exception; MODE_ERROR : exception; NAME_ERROR : exception; USE_ERROR : exception; DEVICE_ERROR : exception; END_ERROR : exception; DATA_ERROR : exception; LAYOUT_ERROR : exception; end IO_EXCEPTIONS; > 14.6 Low Level Input-Output A low level input-output operation is an operation acting on a physical device. Such an operation is handled by using one of the (overloaded) predefined procedures SEND_CONTROL and RECEIVE_CONTROL. A procedure SEND_CONTROL may be used to send control information to a physical device. A procedure RECEIVE_CONTROL may be used to monitor the execution of an input-output operation by requesting information from the physical device. Such procedures are declared in the standard package LOW_LEVEL_IO and have two parameters identifying the device and the data. However, the kinds and formats of the control information will depend on the physical characteristics of the machine and the device. Hence, the types of the parameters are implementation-defined. Overloaded definitions of these procedures should be provided for the supported devices. The visible part of the package defining these procedures is outlined as follows: package LOW_LEVEL_IO is -- declarations of the possible types for DEVICE and DATA; -- declarations of overloaded procedures for these types: procedure SEND_CONTROL (DEVICE : DEVICE_TYPE; DATA : in out DATA_TYPE); procedure RECEIVE_CONTROL (DEVICE : DEVICE_TYPE; DATA : in out DATA_TYPE); end; The bodies of the procedures SEND_CONTROL and RECEIVE_CONTROL for various devices can be supplied in the body of the package LOW_LEVEL_IO. These procedure bodies may be written with code statements. > 14.7 Example of Input-Output The following example shows the use of some of the text input-output facilities in a dialogue with a user at a terminal. The user is prompted to type a color, and the program responds by giving the number of items of that color available in stock, according to an inventory. The default input and output files are used. For simplicity, all the requisite instantiations are given within one subprogram; in practice, a package, separate from the procedure, would be used. with TEXT_IO; use TEXT_IO; procedure DIALOGUE is type COLOR is (WHITE, RED, ORANGE, YELLOW, GREEN, BLUE, BROWN); package COLOR_IO is new ENUMERATION_IO(ENUM => COLOR); package NUMBER_IO is new INTEGER_IO(INTEGER); use COLOR_IO, NUMBER_IO; INVENTORY : array (COLOR) of INTEGER := (20, 17, 43, 10, 28, 173, 87); CHOICE : COLOR; procedure ENTER_COLOR (SELECTION : out COLOR) is begin loop begin PUT("Color selected: "); -- prompts user GET(SELECTION); -- accepts color typed, or raises exception return; exception when DATA_ERROR => PUT("Invalid color, try again. "); -- user has typed new line NEW_LINE(2); -- completes execution of the block statement end; end loop; -- repeats the block statement until color accepted end; begin -- statements of DIALOGUE; NUMBER_IO.DEFAULT_WIDTH := 5; loop ENTER_COLOR(CHOICE); -- user types color and new line SET_COL(5); PUT(CHOICE); PUT(" items available:"); SET_COL(40); PUT(INVENTORY(CHOICE)); -- default width is 5 NEW_LINE; end loop; end DIALOGUE; Example of an interaction (characters typed by the user are italicized): Color selected: Black Invalid color, try again. Color selected: Blue BLUE items available: 173 Color selected: Yellow YELLOW items available: 10