FOPEN

Section: C Library Functions (3)
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BSD mandoc
 

NAME

fopen fdopen freopen - stream open functions  

SYNOPSIS

Fd #include <stdio.h> Ft FILE * Fn fopen char *path char *mode Ft FILE * Fn fdopen int fildes char *mode Ft FILE * Fn freopen char *path char *mode FILE *stream  

DESCRIPTION

The Fn fopen function opens the file whose name is the string pointed to by Fa path and associates a stream with it.

The argument Fa mode points to a string beginning with one of the following sequences (Additional characters may follow these sequences.):

``r ''
Open text file for reading. The stream is positioned at the beginning of the file.
``r+ ''
Open for reading and writing. The stream is positioned at the beginning of the file.
``w ''
Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file.
``w+ ''
Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file.
``a ''
Open for writing. The file is created if it does not exist. The stream is positioned at the end of the file.
``a+ ''
Open for reading and writing. The file is created if it does not exist. The stream is positioned at the end of the file.

The Fa mode string can also include the letter ``b'' either as a third character or as a character between the characters in any of the two-character strings described above. This is strictly for compatibility with St -ansiC and has no effect; the ``b'' is ignored.

Any created files will have mode \*q S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH \*q (0666 ) as modified by the process' umask value (see umask(2)).

Reads and writes may be intermixed on read/write streams in any order, and do not require an intermediate seek as in previous versions of stdio This is not portable to other systems, however; ANSI C requires that a file positioning function intervene between output and input, unless an input operation encounters end-of-file.

The Fn fdopen function associates a stream with the existing file descriptor, Fa fildes . The Fa mode of the stream must be compatible with the mode of the file descriptor.

The Fn freopen function opens the file whose name is the string pointed to by Fa path and associates the stream pointed to by Fa stream with it. The original stream (if it exists) is closed. The Fa mode argument is used just as in the fopen function. The primary use of the Fn freopen function is to change the file associated with a standard text stream ( stderr stdin or stdout )  

RETURN VALUES

Upon successful completion Fn fopen , Fn fdopen and Fn freopen return a FILE pointer. Otherwise, NULL is returned and the global variable errno is set to indicate the error.  

ERRORS

Bq Er EINVAL
The Fa mode provided to Fn fopen , Fn fdopen , or Fn freopen was invalid.

The Fn fopen , Fn fdopen and Fn freopen functions may also fail and set errno for any of the errors specified for the routine malloc(3).

The Fn fopen function may also fail and set errno for any of the errors specified for the routine open(2).

The Fn fdopen function may also fail and set errno for any of the errors specified for the routine fcntl(2).

The Fn freopen function may also fail and set errno for any of the errors specified for the routines open(2), fclose(3) and fflush(3).  

SEE ALSO

open(2), fclose(3), fseek(3), funopen(3)  

STANDARDS

The Fn fopen and Fn freopen functions conform to St -ansiC . The Fn fdopen function conforms to St -p1003.1-88 .

 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
SEE ALSO
STANDARDS
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Time: 19:42:00 GMT, December 25, 2022