rand(3C) Standard C Library Functions 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 successive pseudo-random num-
bers 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 subsequent 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. If
rand_r() is called with the same initial value for the object pointed to by seed and that object is not modified between successive calls
to rand_r(), the same sequence as that produced by calls to rand() will be generated.
The rand() and srand() functions provide per-process pseudo-random streams shared by all threads. The same effect can be achieved if all
threads call rand_r() with a pointer to the same seed object. The rand_r() function allows a thread to generate a private pseudo-random
stream by having the seed object be private to the thread.
USAGE
The spectral properties of rand() are limited. The drand48(3C) function provides a better, more elaborate random-number generator.
When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should be used only in mul-
tithreaded applications.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |Safe |
+-----------------------------+-----------------------------+
SEE ALSO
drand48(3C), attributes(5), standards(5)
SunOS 5.11 19 May 2004 rand(3C)
