#include <math.h> double pow(double x, double y);
float powf(float x, float y);
long double powl(long double x, long double y);
Link with -lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
powf(), powl():
If x is a finite value less than 0, and y is a finite noninteger, a domain error occurs, and a NaN is returned.
If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathematically correct sign.
If result underflows, and is not representable, a range error occurs, and 0.0 is returned.
Except as specified below, if x or y is a NaN, the result is a NaN.
If x is +1, the result is 1.0 (even if y is a NaN).
If y is 0, the result is 1.0 (even if x is a NaN).
If x is +0 (-0), and y is an odd integer greater than 0, the result is +0 (-0).
If x is 0, and y greater than 0 and not an odd integer, the result is +0.
If x is -1, and y is positive infinity or negative infinity, the result is 1.0.
If the absolute value of x is less than 1, and y is negative infinity, the result is positive infinity.
If the absolute value of x is greater than 1, and y is negative infinity, the result is +0.
If the absolute value of x is less than 1, and y is positive infinity, the result is +0.
If the absolute value of x is greater than 1, and y is positive infinity, the result is positive infinity.
If x is negative infinity, and y is an odd integer less than 0, the result is -0.
If x is negative infinity, and y less than 0 and not an odd integer, the result is +0.
If x is negative infinity, and y is an odd integer greater than 0, the result is negative infinity.
If x is negative infinity, and y greater than 0 and not an odd integer, the result is positive infinity.
If x is positive infinity, and y less than 0, the result is +0.
If x is positive infinity, and y greater than 0, the result is positive infinity.
If x is +0 or -0, and y is an odd integer less than 0, a pole error occurs and HUGE_VAL, HUGE_VALF, or HUGE_VALL, is returned, with the same sign as x.
If x is +0 or -0, and y is less than 0 and not an odd integer, a pole error occurs and +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, is returned.
The following errors can occur:
| Interface | Attribute | Value |
| pow(), powf(), powl() | Thread safety | MT-Safe |
The variant returning double also conforms to SVr4, 4.3BSD, C89.
In glibc 2.9 and earlier, when a pole error occurs, errno is set to EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing.
If x is negative, then large negative or positive y values yield a NaN as the function result, with errno set to EDOM, and an invalid (FE_INVALID) floating-point exception. For example, with pow(), one sees this behavior when the absolute value of y is greater than about 9.223373e18.
In version 2.3.2 and earlier, when an overflow or underflow error occurs, glibc's pow() generates a bogus invalid floating-point exception (FE_INVALID) in addition to the overflow or underflow exception.