/C

# isinf

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

Determines if the given floating-point number `arg` is positive or negative infinity. The macro returns an integral value.

`FLT_EVAL_METHOD` is ignored: even if the argument is evaluated with more range and precision than its type, it is first converted to its semantic type, and the classification is based on that.

### Parameters

 arg - floating-point value

### Return value

Nonzero integral value if `arg` has an infinite value, `​0​` otherwise.

### Example

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

int main(void)
{
printf("isinf(NAN)         = %d\n", isinf(NAN));
printf("isinf(INFINITY)    = %d\n", isinf(INFINITY));
printf("isinf(0.0)         = %d\n", isinf(0.0));
printf("isinf(DBL_MIN/2.0) = %d\n", isinf(DBL_MIN/2.0));
printf("isinf(1.0)         = %d\n", isinf(1.0));
printf("isinf(exp(800))    = %d\n", isinf(exp(800)));
}```

Possible output:

```isinf(NAN)         = 0
isinf(INFINITY)    = 1
isinf(0.0)         = 0
isinf(DBL_MIN/2.0) = 0
isinf(1.0)         = 0
isinf(exp(800))    = 1```
• C17 standard (ISO/IEC 9899:2018):
• 7.12.3.3 The isinf macro (p: 172)
• C11 standard (ISO/IEC 9899:2011):
• 7.12.3.3 The isinf macro (p: 236)
• C99 standard (ISO/IEC 9899:1999):
• 7.12.3.3 The isinf macro (p: 217)

 fpclassify (C99) classifies the given floating-point value (function macro) isfinite (C99) checks if the given number has finite value (function macro) isnan (C99) checks if the given number is NaN (function macro) isnormal (C99) checks if the given number is normal (function macro) C++ documentation for `isinf`