NAME
rand, srand,
sranddev, rand_r —
bad random number generator
LIBRARY
library “libc”
SYNOPSIS
#include
<stdlib.h>
void
srand(unsigned
seed);
void
sranddev(void);
int
rand(void);
int
rand_r(unsigned
*ctx);
DESCRIPTION
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 the
random(4) random number device which returns good random numbers.
However, the rand() function still remains
unsuitable for cryptographic use.
The
rand_r()
function provides the same functionality as rand().
A pointer to the context value ctx must be supplied by
the caller.
SEE ALSO
STANDARDS
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.