stdlib —
standard library definitions
The <stdlib.h> header defines
  the following types and macros:
  - NULL- an implementation-defined null pointer constant;
- size_t and wchar_t - integer
      types described in
      stddef(3);
- div_t, ldiv_t, and
      lldiv_t - structures that are returned by the
      div(3),
      ldiv(3), and
      lldiv(3) functions,
      respectively;
- RAND_MAX- a macro which expands to an integer constant that is the maximum value
      returned by the rand(3)
      function;
- MB_CUR_MAX- an integer expression of type size_t whose value
      is the maximum number of bytes in a character specified by the current
      locale; and
- EXIT_SUCCESSand- EXIT_FAILURE- macros which expand to integer
      constants suitable for use as an argument to the
      exit(3) function.
The <stdlib.h>
    header also prototypes several important functions such as
    abort(3),
    atoi(3),
    bsearch(3),
    free(3),
    malloc(3), and
    strtol(3).
As described here, the
  <stdlib.h> header conforms to
  ISO/IEC 9899:1999 (“ISO C99”) and
  IEEE Std 1003.1-2001 (“POSIX.1”).
In the current form the
  <stdlib.h> header was
  introduced in NetBSD 0.8.