March 5, 2004 ISNAN 3

### NAME

isnan - test for not-a-number

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```int` isnan(```real-floating x`)

### DESCRIPTION

The isnan(``) macro determines whether its argument ```x` is not-a-number (``NaN''). An argument represented in a format wider than its semantic type is converted to its semantic type first. The determination is then based on the type of the argument.

#### IEEE 754

It is determined whether the value of ```x` is a NaN.

#### VAX

NaNs are not supported.

### RETURN VALUES

The isnan(``) macro returns a non-zero value if the value of ```x` is a NaN. Otherwise 0 is returned.

### SEE ALSO

fpclassify(3), isfinite(3), isinf(3), isinff(3), isnanf(3), isnormal(3), math(3), signbit(3)

### STANDARDS

The isnan(``) macro conforms to ISO/IEC 9899:1999 (``ISO C99'') .