random_r, srandom_r, initstate_r, setstate_r — reentrant random number generator


#include <stdlib.h>
int random_r( struct random_data *buf,
  int32_t *result);
int srandom_r( unsigned int seed,
  struct random_data *buf);
int initstate_r( unsigned int seed,
  char *statebuf,
  size_t statelen,
  struct random_data *buf);
int setstate_r( char *statebuf,
  struct random_data *buf);
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
random_r(), srandom_r(), initstate_r(), setstate_r():


These functions are the reentrant equivalents of the functions described in random(3). They are suitable for use in multithreaded programs where each thread needs to obtain an independent, reproducible sequence of random numbers.

The random_r() function is like random(3), except that instead of using state information maintained in a global variable, it uses the state information in the argument pointed to by buf. The generated random number is returned in the argument result.

The srandom_r() function is like srandom(3), except that it initializes the seed for the random number generator whose state is maintained in the object pointed to by buf, instead of the seed associated with the global state variable.

The initstate_r() function is like initstate(3) except that it initializes the state in the object pointed to by buf, rather than initializing the global state variable.

The setstate_r() function is like setstate(3) except that it modifies the state in the object pointer to by buf, rather than modifying the global state variable.


All of these functions return 0 on success. On error, −1 is returned, with errno set to indicate the cause of the error.



A state array of less than 8 bytes was specified to initstate_r().


The statebuf or buf argument to setstate_r() was NULL.


The buf or result argument to random_r() was NULL.


These functions are nonstandard glibc extensions.


drand48(3), rand(3), random(3)


This page is part of release 3.52 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at−pages/.

  Copyright 2008 Michael Kerrisk <>

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