Pointers

A pointer type variable holds the address of a data object or a function. A pointer can refer to an object of any one data type; it cannot refer to a bit field or a reference.

Some common uses for pointers are:

To access dynamic data structures such as linked lists, trees, and queues.
To access elements of an array or members of a structure or C++ class.
To access an array of characters as a string.
To pass the address of a variable to a function. (In C++, you can also use a reference to do this.) By referencing a variable through its address, a function can change the contents of that variable.

The z/OS® XL C compiler supports only the pointers that are obtained in one of the following ways:

Directly from the return value of a library function which returns a pointer
As an address of a variable
From constants that refer to valid addresses or from the NULL constant
Received as a parameter from another C function
Directly from a call to a service in the z/OS IBM Language Environment® that allocates storage, such as CEEGTST

Any bitwise manipulation of a pointer can result in undefined behavior. End C only

Note that the placement of the type qualifiers volatile and const affects the semantics of a pointer declaration. If either of the qualifiers appears before the *, the declarator describes a pointer to a type-qualified object. If either of the qualifiers appears between the * and the identifier, the declarator describes a type-qualifed pointer.

The following table provides examples of pointer declarations.

Table 1. Pointer declarations
Declaration	Description
`long *pcoat;`	`pcoat` is a pointer to an object having type `long`
`extern short * const pvolt;`	`pvolt` is a constant pointer to an object having type `short`
`extern int volatile *pnut;`	`pnut` is a pointer to an `int` object having the `volatile` qualifier
`float * volatile psoup;`	`psoup` is a `volatile` pointer to an object having type `float`
`enum bird *pfowl;`	`pfowl` is a pointer to an enumeration object of type `bird`
`char (*pvish)(void);`	`pvish` is a pointer to a function that takes no parameters and returns a `char`
`nullptr_t pnull;`	`pnull` is a null pointer that does not point to any valid object or function.
`int (*__fdptr pfunc)(float);`	`pfunc` is a function pointer to a DLL like function that takes a `float` argument and returns an `int`. Note: The `__fdptr` qualifier can be used only when the METAL compiler option is specified.