OSF

NAME

rand, rand_r, srand − Generates pseudo-random numbers

LIBRARY

Standard C Library (libc.a),
Berkeley Compatibility Library (libbsd.a)
Reentrant Library (libc_r.a)

SYNOPSIS

#include <stdlib.h> int rand (void); int rand_r(
unsigned int ∗seedptr,
int ∗randval ); void srand (
unsigned int seed);

PARAMETERS

seedSpecifies an initial seed value. 

seedptrPoints to a seed value, updated at each call. 

randvalPoints to a place to store the random number. 

DESCRIPTION

The rand() function returns successive pseudo-random 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 rand_r() function is the reentrant version of the rand() function, for use with multi-threaded applications.  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. 

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. 

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 multi-threaded 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 to231 - 1, rather than 0 to215 - 1, and can be used by compiling 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 rand(  )
{ next = next ∗ 1103515245 + 12345; return (  (next >>16) & RAND_MAX);
} void srand (seed)
int seed;
{ next = seed
}

AES Support Level:
Full use (rand(), srand())

RETURN VALUES

The rand() function returns the next pseudo-random number in the sequence. 

Upon successful completion, 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

If the rand_r() function fails, errno may be set to the following value:

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

RELATED INFORMATION

Functions: drand48(3), random(3)