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
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.
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. |