rand(S)

Syntax

#include  <stdlib.h>

int rand (void);
void srand(unsigned int seed);

Description

srand- reset random-number generator

The rand function uses a multiplicative congruential random-number generator with period 2^32 that returns successive pseudo-random numbers in the range from 0 to (2^15)-1.

The srand function can be called at any time to reset the random-number generator to a random starting point. The generator is initially seeded with a value of 1.

Notes

The following functions define the semantics of the functions rand and srand.

   static unsigned long int next = 1;
   int rand()
   {
        next = next * 1103515245 + 12345;
        return ((unsigned int)(next/65536) % 32768);
   }
   void srand(seed)
   unsigned int seed;
   {
        next = seed;
   }

Specifying the semantics makes it possible to reproduce the behavior of programs that use pseudo-random sequences. This facilitates the testing of portable applications in different implementations.

See also

Standards conformance

X/Open Portability Guide, Issue 3, 1989 ;
ANSI X3.159-1989 Programming Language -- C ;
IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1) ;
and NIST FIPS 151-1 .