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4.2  Objects & Messages

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Thus far we have not declared any variables whose type is a class.  Such variables are called OBJECTS.  In TC (but not in C++) it is illegal to declare an identifier which is itself an object.  Rather, we must declare an identifier which is a pointer to an object of the desired class.  Since this is understood for all TC objects, we will not bother to indicate in the identifier name that it is a pointer as we usually do (e.g.  float  *f_ptr).  In fact, we will refer to the pointer as though it were the object itself.

    Student  *jack;       /* note: 'struct' is not needed */

Recall that defining a pointer to a data type allocates space only for a machine address; it does not allocate space for the data type - in this case a Student object - itself.  In C++ the 'new' operator allocates space for the instance variables of an object and returns a pointer to this space.  TC uses the new() function for this purpose.

    jack = new(Student);    /* in C++ the parentheses are not required */

Unlike the case with variables having "automatic" storage class*, space allocated by the new() function (or in C++ the 'new' operator) is not deallocated upon completion




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Automatic storage

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Automatic storage - p77

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