stddef.h header provides fundamental type aliases and macros. Many of these definitions also appear in other headers.
Excluding type aliases
wchar_t and function-like macro
- Alias for:
unsigned long int
sizeofoperator returns a
size_tvalue. It is widely used in the standard library to represent sizes and counts.
- Expands to
Macro for a null pointer. It has three primary use cases:
- To initialise a pointer variable before assigning it a valid memory address.
- To return from a function when no valid memory address can be returned, e.g. for error handling.
- To pass as a function argument when it is not desired to pass a valid memory address.