Raise a number to a given power
#include <math.h>
double pow( double x,
double y );
float powf( float x,
float y );
long double powl( long double x,
long double y );
The pow(), powf(), and powl() functions compute x raised to the power of y.
To check for error situations, use feclearexcept() and fetestexcept(). For example:
The value of xy.
| If x is: | And y is: | These functions return: | Errors: |
|---|---|---|---|
| < 0.0, but finite | Finite non-integer | NaN | FE_INVALID |
| 0.0 | < 0.0 | Inf | FE_DIVBYZERO |
| 1.0 | Any value, including NaN | 1.0 | — |
| Not 1.0 | NaN | NaN | — |
| Any value, including 0.0 and NaN | ±0.0 | 1.0, but note that the correct mathematical result for 0.00.0 is undefined | — |
| NaN | Nonzero | NaN | — |
| ±0.0 | Any odd integer > 0.0 | 0.0, with the same sign as x | — |
| ±0.0 | Any even integer > 0.0 | 0.0 | — |
| -1.0 | ±Inf | 1.0 | — |
| |x| < 1.0 | -Inf | Inf | — |
| |x| > 1.0 | -Inf | 0.0 | — |
| |x| < 1.0 | Inf | 0.0 | — |
| |x| > 1.0 | Inf | Inf | — |
| -Inf | An odd integer < 0.0 | -0.0 | — |
| -Inf | A non-odd integer < 0.0 | +0.0 | — |
| -Inf | An odd integer > 0.0 | -Inf | — |
| -Inf | A non-odd integer > 0.0 | Inf | — |
| Inf | < 0.0 | 0.0 | — |
| Inf | > 0.0 | Inf | — |
| If the correct value would cause: | These functions return: | Errors: |
|---|---|---|
| Overflow | Inf | FE_OVERFLOW |
| Underflow and is representable | The correct value, after rounding | FE_UNDERFLOW |
These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.
#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>
int main( void )
{
int except_flags;
feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", pow( 1.5, 2.5 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}
return EXIT_SUCCESS;
}
produces the output:
2.755676
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | No |
| Thread | Yes |