rand(3C)
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 2**32 that returns suc-
cessive 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 sub-
sequent 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.
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 applica-
tions.
When compiling multithreaded applications, the _REENTRANT
flag must be defined on the compile line. This flag should
only be used in multithreaded applications.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | See USAGE above. |
|_____________________________|_____________________________|
SEE ALSO
drand48(3C), attributes(5)
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