##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# isnan

From cppreference.com
< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
#define isnan(arg) /* implementation defined */ |  | (since C99)

Determines if the given floating point number `arg` is not-a-number (`NaN`). The macro returns an integral value.

### [edit] Parameters

arg | - | floating point value

### [edit] Return value

Nonzero integral value if `arg` is NaN, ​0​ otherwise.

### [edit] Example

Run this code

    #include <stdio.h>
    #include <math.h>
    #include <float.h>

    int main(void)
    {
        printf("isnan(NAN)         = %d\n", isnan(NAN));
        printf("isnan(INFINITY)    = %d\n", isnan(INFINITY));
        printf("isnan(0.0)         = %d\n", isnan(0.0));
        printf("isnan(DBL_MIN/2.0) = %d\n", isnan(DBL_MIN/2.0));
        printf("isnan(1.0)         = %d\n", isnan(1.0));

        return 0;
    }

Possible output:

    isnan(NAN)         = 1
    isnan(INFINITY)    = 0
    isnan(0.0)         = 0
    isnan(DBL_MIN/2.0) = 0
    isnan(1.0)         = 0

### [edit] See also

fpclassify (C99) | classifies the given floating-point value (function) [edit]
isfinite (C99) | checks if the given number has finite value (function) [edit]
isinf (C99) | checks if the given number is infinite (function) [edit]
isnormal (C99) | checks if the given number is normal (function) [edit]
isunordered (C99) | checks if two floating-point values are unordered (function) [edit]
C++ documentation for isnan

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=c/numeric/math/isnan&oldid=70469"