rand_s
The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at rand_s.
Generates a pseudorandom number. A version of rand with security enhancements as described in Security Features in the CRT.
errno_t rand_s( unsigned int* randomValue);
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. If the function fails for any other reason, *randomValue is set to 0.
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.
| Routine | Required header |
|---|---|
rand_s | <stdlib.h> |
For more information, see Compatibility.
// 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 + 1 ) * 10.0) + 1);
}
printf_s("\n");
// Display 10 random doubles in [0, 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 + 1) * max );
}
}
10 4 5 2 8 2 5 6 1 1 32.6617 29.4471 11.5413 6.41924 20.711 60.2878 61.0094 20.1222 80.9192 65.0712