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rand(3)
NAME
  rand, rand_r, srand - Generate pseudorandom numbers

SYNOPSIS
  #include <stdlib.h>

  int rand(
	  void );

  int rand_r(
	  unsigned int *seedptr );

  void srand(
	  unsigned int seed );

  The following function does not conform to current standards and is
  supported only for backward compatibility:

  int rand_r(
	  unsigned int *seedptr,
	  int *randval );

LIBRARY
  Standard C Library (libc)

  Berkeley Compatibility Library (libbsd.a)

STANDARDS
  Interfaces documented on this reference page conform to industry  standards
  as follows:

  rand_r():  POSIX.1c

  rand(), srand():  XPG4, XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  seed
      Specifies an initial seed value.

  seedptr
      Points to a seed value, updated at each call.

  randval
      Points to a place to store the random number.

DESCRIPTION
  The rand() function returns successive pseudorandom numbers in the range
  from 0 (zero) to RAND_MAX.  The sequence of values returned depends on the
  seed value set with the srand() function.  If rand() is called before any
  calls to srand() have been made, the same sequence will be generated as
  when srand() is first called with a seed value of 1.

  The srand() function resets the random-number generator to a random
  starting point. The generator is initially seeded with  a value of 1.

  The rand() function is a very simple	random-number generator. Its spectral
  properties, the mathematical	measurement of how random the number sequence
  is, are somewhat weak.

  [POSIX]  The rand_r() function is the reentrant version of the rand()
  function.  The rand_r() function places the seed value at the address
  pointed to by seedptr,  and returns the random number.

  [Tru64 UNIX]	The obsolete version of the rand_r() function places  the
  seed value at the address pointed to by seedptr, and	places the random
  number at the address pointed to by randval.

  See the drand48() and random() functions for more elaborate random-number
  generators that have better spectral properties.

NOTES
  The rand() function is not supported for multithreaded applications.
  Instead, its reentrant equivalent, rand_r(), should be used with multiple
  threads.

  The BSD version of the rand() function returns a number in the range 0 to
  (2^31)-1, rather than 0 to (2^15)-1, and can be used by compiling the code
  with the Berkeley Compatibility Library (libbsd.a).

  There are better random number generators, as noted above; however, the
  rand() and srand() functions are the interfaces defined for the ANSI C
  library.

  The following functions define the semantics of the rand() and srand()
  functions, and are included here to facilitate porting applications from
  different implementations:

       static unsigned int next = 1;
       int myrand(void)
       {
	       next = next * 1103515245 + 12345;
	       return (	 (next >>16) & RAND_MAX);
       }
       void mysrand (unsigned int seed)
       {
       next = seed
       }

RETURN VALUES
  The rand() function returns the next pseudorandom number in the sequence.

  [POSIX]  The rand_r function returns the next random number in the
  sequence.

  [Tru64 UNIX]	Upon successful completion, the obsolete version of the
  rand_r() function returns a value of 0 (zero). Otherwise, -1 is returned
  and errno is set to indicate the error.

  The srand() function returns no value.

ERRORS
  [Tru64 UNIX]	If the rand_r() function fails, errno may be set to the
  following value:

  [EINVAL]
      Either seedptr or randval is a null pointer.

SEE ALSO
  Functions: drand48(3), random(3)

  Standards: standards(5)

Index for Section 3

Alphabetical listing for R

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