NAN

#define NAN /* implementation-defined */

The macro NAN expands to a constant expression of type float, which evaluates to a quiet not-a-number (QNaN) value.

If the implementation does not support QNaNs for the type float, this macro is not defined.

Notes

There are many different NaN values, differentiated by their payloads and their sign bits. The contents of the payload and the sign bit of the NaN generated by the macro NAN are implementation-defined.

Example

#include <float.h> // since C23
#include <inttypes.h>
#include <math.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>

int main(void)
{
    const double f = NAN;
    uint64_t fn;
    memcpy(&fn, &f, sizeof f);
    printf("NAN:   %f %" PRIx64 "\n", f, fn);
}

NAN:   nan 7ff8000000000000

References

See also