View source for c/numeric/math/NAN

{{title|NAN}}
{{c/numeric/math/navbar}}
{{dcl begin}}
{{dcl header|math.h}}
{{dcl|since=c99|
#define NAN /*implementation defined*/
}}
{{dcl end}}

The macro {{tt|NAN}} expands to a constant expression of type {{c|float}}, which evaluates to a quiet not-a-number (QNaN) value. If the implementation does not support QNaNs, this macro constant is not defined.

The style used to print a NaN is implementation-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 {{tt|NAN}} are implementation-defined.

===Example===
Show style used to print a NaN and IEEE format.
{{example
|code=
#include <inttypes.h>
#include <math.h>
#include <stdint.h>
#include <stdio.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);
}
|p=true
|output=
NAN:   nan 7ff8000000000000
}}

===References===
{{ref std c23}}
{{ref std|section=7.12/5|title=NAN|p=TBD}}
{{ref std|section=F.10/11/13|title=NAN|p=TBD}}
{{ref std end}}
{{ref std c17}}
{{ref std|section=7.12/5|title=NAN|p=TBD}}
{{ref std|section=F.10/11/13|title=NAN|p=TBD}}
{{ref std end}}
{{ref std c11}}
{{ref std|section=7.12/5|title=NAN|p=232}}
{{ref std|section=F.10/11/13|title=NAN|p=518}}
{{ref std end}}
{{ref std c99}}
{{ref std|section=7.12/5|title=NAN|p=213}}
{{ref std|section=F.9/11/13|title=NAN|p=455}}
{{ref std end}}

===See also===
{{dsc begin}}
{{dsc inc|c/numeric/math/dsc fnan}}
{{dsc inc|c/numeric/math/dsc isnan}}
{{dsc see cpp|cpp/numeric/math/NAN}}
{{dsc end}}

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