rand() – rand_r() — Generate Random Number
Format
#include <stdlib.h>
int rand(void);
int rand_r(unsigned int *seed);
Language Level
ANSI
Threadsafe
No
rand() is not threadsafe, but rand_r() is.
Description
The
rand()
function
generates a pseudo-random integer in the range 0 to RAND_MAX (macro
defined in <stdlib.h>). Use the srand()
function before
calling rand()
to
set a starting point for the random number generator. If you do not
call the srand()
function
first, the default seed is 1. Note: The
rand_r()
function
is the restartable version of rand()
.Return Value
The rand()
function
returns a pseudo-random number.
Example
This example prints the first 10
random numbers generated.
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
int x;
for (x = 1; x <= 10; x++)
printf("iteration %d, rand=%d\n", x, rand());
}
/********************* Output should be similar to: ************
iteration 1, rand=16838
iteration 2, rand=5758
iteration 3, rand=10113
iteration 4, rand=17515
iteration 5, rand=31051
iteration 6, rand=5627
iteration 7, rand=23010
iteration 8, rand=7419
iteration 9, rand=16212
iteration 10, rand=4086
*/