rand_s

rand_s

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Microsoft Visual Studio 2005/.NET Framework 2.0

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Run-Time Library Reference

rand_s

Generates a pseudorandom number. A version of rand with security enhancements as described in Security Enhancements in the CRT.

errno_t rand_s(   unsigned int* randomValue);

Return Value

Zero if successful, otherwise, an error code. If the input pointer randomValue is a null pointer, the function invokes an invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, the function returns EINVAL and sets errno to EINVAL.

Remarks

The rand_s function writes a pseudorandom integer in the range 0 to UINT_MAX to the input pointer. The rand_s function uses the operating system to generate cryptographically secure random numbers. It does not use the seed generated by the srand function, nor does it affect the random number sequence used by rand.

The rand_s function requires that constant _CRT_RAND_S be defined prior to the inclusion statement for the function to be declared, as in the following example:

#define _CRT_RAND_S
#include <stdlib.h>

rand_s depends on the RtlGenRandom API, which is only available in Windows XP and later.

Requirements

Routine	Required header	Compatibility
rand_s	<stdlib.h>	Windows XP Home Edition, Windows XP Professional, Windows Server 2003

For more information, see Compatibility.

Example

// crt_rand_s.c
// This program illustrates how to generate random
// integer or floating point numbers in a specified range.

// Remembering to define _CRT_RAND_S prior
// to inclusion statement.
#define _CRT_RAND_S

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>

int main( void )
{
    int             i;
    unsigned int    number;
    double          max = 100.0;
    errno_t         err;

    // Display 10 random integers in the range [ 1,10 ].
    for( i = 0; i < 10;i++ )
    {
        err = rand_s( &number );
        if (err != 0)
        {
            printf_s("The rand_s function failed!\n");
        }
        printf_s( "  %u\n", (unsigned int) ((double)number /
                          (double) UINT_MAX * 10.0) + 1);
    }

    printf_s("\n");

    // Display 10 random doubles between 0 and max.
    for (i = 0; i < 10;i++ )
    {
        err = rand_s( &number );
        if (err != 0)
        {
            printf_s("The rand_s function failed!\n");
        }
        printf_s( "  %g\n", (double) number / 
                          (double) UINT_MAX * max );
    }
}

Sample Output

.NET Framework Equivalent

System::Random Class

Reference

Floating-Point Support
srand