RAND_MAX

 

C

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Error handling

Dynamic memory management

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Technical Specifications

Symbol index

 

Numerics

Common mathematical functions

Floating-point environment (C99)

Pseudo-random number generation

Complex number arithmetic (C99)

Type-generic math (C99)

 

Pseudo-random number generation

rand

srand

RAND_MAX

 

Defined in header <stdlib.h>
#define RAND_MAX /*implementation defined*/

Expands to an integer constant expression equal to the maximum value returned by the function rand(). This value is implementation dependent. It's guaranteed that this value is at least 32767.

Example

Run this code

#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
 
int main(void)
{
    srand(time(NULL)); // use current time as seed for random generator
    printf("RAND_MAX: %i\n", RAND_MAX);
    printf("INT_MAX: %i\n", INT_MAX);
    printf("Random value on [0,1]: %f\n", (double)rand() / RAND_MAX);
}

Possible output:

RAND_MAX: 2147483647
INT_MAX: 2147483647
Random value on [0,1]: 0.362509

References

• C17 standard (ISO/IEC 9899:2018):

• 7.22/3 General utilities <stdlib.h> (p: 248)

• C11 standard (ISO/IEC 9899:2011):

• 7.22/3 General utilities <stdlib.h> (p: 340)

• C99 standard (ISO/IEC 9899:1999):

• 7.20/3 General utilities <stdlib.h> (p: 306)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.10 GENERAL UTILITIES <stdlib.h>

See also

rand	generates a pseudo-random number (function)
srand	seeds pseudo-random number generator (function)