rand(3C)

NAME | SYNOPSIS | DESCRIPTION | USAGE | ATTRIBUTES | SEE ALSO | NOTES

NAME

rand, srand, rand_r- simple random-number generator

SYNOPSIS

#include <stdlib.h>

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

DESCRIPTION

The rand() function uses a multiplicative congruential random-number generator with period 2³² that returns successive pseudo-random numbers in the range of 0 to RAND_MAX (defined in <stdlib.h> ).

The srand() function uses the argument seed as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to rand() . If srand() is then called with the same seed value, the sequence of pseudo-random numbers will be repeated. 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 has the same functionality as rand() except that a pointer to a seed seed must be supplied by the caller. The seed to be supplied is not the same seed as in srand() .

USAGE

The spectral properties of rand() are limited. The drand48(3C) function provides a better, more elaborate random-number generator.

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
MT-Level	See NOTES below.

SEE ALSO

drand48(3C) , attributes(5)

NOTES

The rand_r() function is as proposed in the POSIX.4a Draft #6 document, and is subject to change to be compliant with the standard when it is accepted.

The rand() is unsafe in multithreaded applications. The rand_r() function is MT-Safe, and should be used instead. The srand() function is unsafe in multithreaded applications.

When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in multithreaded applications.

SunOS 5.8  Last Revised 29 Dec 1996

NAME | SYNOPSIS | DESCRIPTION | USAGE | ATTRIBUTES | SEE ALSO | NOTES