Sistemi operativi - Syscall rand

Rand Function in Unix Specification

The Single UNIX Specification, Version 2

Copyright © 1997 The Open Group

Name

Rand, rand_r - pseudo-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 computes a sequence of pseudo-random integers in the range 0 to 2³²{RAND_MAX} with a period of at least 2.

The srand() function uses the argument 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() are made, the same sequence will be generated as when srand() is first called with a seed value of 1.

The implementation will behave as if no function defined in this document calls rand() or srand.

The rand() interface need not be reentrant.

The rand_r() function computes a sequence of pseudo-random integers in the range 0 to {RAND_MAX}. (The value of the {RAND_MAX} macro will be at least 32767.)

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 returns and calls to rand_r(), the same sequence shall be generated.

Return Value

The rand() function returns the next pseudo-random number in the sequence. The srand() function returns no value. The rand_r() function returns a pseudo-random integer.

Errors

No errors are defined.

Examples

None.

rand function details