Stdlib.h

stdlib.h is the header of the general purpose standard library of C programming language which includes functions involving memory allocation, process control, conversions and others. It is compatible with C++ and is known as cstdlib in C++. The name "stdlib" stands for standard library.

Member functions

Members of the stdlib.h can be classified into the following categories: conversion, memory, process control, sort and search, mathematics.

Member constants

The stdlib.h and stddef.h header files define the macro NULL, which yields a null pointer constant, and represents a pointer value that is guaranteed not to point to a valid address in memory. NULL may be defined as a constant expression equal to int zero, long int zero, or zero cast to a void * pointer:

#define NULL 0 #define NULL 0L #define NULL ((void *) 0)

Note: Although the null pointer constant is always represented in C by the symbolic constant 0 or by 0 cast to a void pointer, the actual bit representation of such a pointer is system-specific and might not be all-bits-zero.

Member data types

The stdlib.h library is required to define a datatype called size_t [As per the C99 standard ISO/IEC 9899, Section "7.20 General utilities " (point number 2) and Appendix "B.19 General utilities ". The definition can also provided by stddef.h if one wants to avoid including the whole of stdlib.] which is used to represent the size of an object. Library functions that take sizes expect them to be of type size_t, and the sizeof operator evaluates to size_t.

The actual type of size_t is platform-dependent; a common mistake is to assume size_t is the same as unsigned int, which can lead to programming errors [http://www.gamedev.net/reference/programming/features/20issues64bit/] ,particularly as 64-bit architectures become more prevalent.

Two less widely used datatypes, div_t and ldiv_t, are also defined. They are the return types of the div and ldiv functions. The standard defines them as:

typedef struct { int quot, rem;} div_t;

typedef struct { long int quot, rem;} ldiv_t;

Nonstandard functions

itoa is a common function that is included in many implementations of stdlib.h, but the standard does not define the function. It may have been included because of its appearance in "The C Programming Language". The same effect can be achieved with sprintf, which is defined in the standard.

ee also

*stdio.h
*C standard library

References

* [http://www.cplusplus.com/ref/cstdlib/ stdlib.h summary on cplusplus.com] , accessed in February 2006.
* [http://www.embedded.com/columns/programmingpointers/200900195?pgno=1 Why size_t matters]