random() — A better random-number generator

Standards

Format

#define _XOPEN_SOURCE_EXTENDED 1
#include <stdlib.h>

long random(void);

General description

The random() function uses a nonlinear additive feedback random-number generator employing a default state array size of 31 long integers to return successive pseudo-random numbers in the range from 0 to 2³¹-1. The period of this random-number generator is approximately 16x(2³¹-1). The size of the state array determines the period of the random-number generator. Increasing the state array size increases the period.

With 256 bytes of state information, the period of the random-number generator is greater than 2⁶⁹.

Like rand(), random() produces by default a sequence of numbers that can be duplicated by calling srandom() with 1 as the seed. The state information for the random functions is maintained on a per-thread basis. For example, calls to srandom() in one thread will have no effect on the numbers generated by calls to random() in another thread.

Returned value

random() returns the generated pseudo-random number.

Related information

• stdlib.h
• drand48() — Pseudo-random number generator
• initstate() — Initialize generator for random()
• setstate() — Change generator for random()
• srandom() — Use seed to initialize generator for random()