RAND(3) BSD Library Functions Manual RAND(3)
rand, srand, sranddev, rand_r -- bad random number generator
Standard C Library (libc, -lc)
The functions described in this manual page are not cryptographically secure. Cryptographic applications should use arc4random(3) instead.
These interfaces are obsoleted by random(3).
The rand() 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 srand() 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 sranddev() function initializes a seed using pseudo-random numbers obtained from the kernel.
The rand_r() function provides the same functionality as rand(). A pointer to the context value ctx must be supplied by the caller.
For better generator quality, use random(3) or lrand48(3).
arc4random(3), lrand48(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.
April 2, 2013 BSD