RAND(3) Library Functions Manual RAND(3)

rand, rand_r, srand, sranddev — bad random number generator

Standard C Library (libc, -lc)

#include <stdlib.h>

int
rand(void);

int
rand_r(unsigned *seed);

void
srand(unsigned seed);

void
sranddev(void);

These interfaces are obsoleted by arc4random(3).

The () function computes a sequence of pseudo-random integers in the range of 0 to RAND_MAX (as defined by the header file <stdlib.h>).

The () function sets its argument seed as the seed for a new sequence of pseudo-random numbers to be returned by rand(). These sequences are repeatable by calling srand() with the same seed value.

If no seed value is provided, the functions are automatically seeded with a value of 1.

The () function initializes a seed, using the random(4) random number device which returns good random numbers. However, the rand() function still remains unsuitable for cryptographic use.

The () function provides the same functionality as rand(). A pointer to the context value seed must be supplied by the caller.

arc4random(3), random(3), random(4)

The rand() and srand() functions conform to ISO/IEC 9899:1990 (“ISO C90”).

The rand_r() function is as proposed in the POSIX.4a Draft #6 document.

May 25, 1999 Mac OS X 12