std::sqrt
Defined in header <cmath>
|
||
float sqrt( float arg ); |
(1) | |
double sqrt( double arg ); |
(2) | |
long double sqrt( long double arg ); |
(3) | |
double sqrt( Integral arg ); |
(4) | (since C++11) |
Computes the square root of arg
.
Parameters
arg | - | Value of a floating-point or Integral type |
Return value
If no errors occur, square root of arg
(√arg), is returned.
If a domain error occurs, an implementation-defined value is returned (NaN where supported)
If a range error occurs due to underflow, the correct result (after rounding) is returned.
Error handling
Errors are reported as specified in math_errhandling
Domain error occurs if arg
is less than zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- If the argument is less than -0, FE_INVALID is raised and NaN is returned.
- If the argument is +∞ or ±0, it is returned, unmodified.
- If the argument is NaN, NaN is returned
Notes
std::sqrt
is required by the IEEE standard to be exact. The only other operations required to be exact are the arithmetic operators and the function std::fma. After rounding to the return type (using default rounding mode), the result of std::sqrt
is indistinguishable from the infinitely precise result. In other words, the error is less than 0.5 ulp. Other functions, including std::pow, are not so constrained.
Example
#include <iostream> #include <cmath> #include <cerrno> #include <cfenv> #include <cstring> #pragma STDC FENV_ACCESS ON int main() { // normal use std::cout << "sqrt(100) = " << std::sqrt(100) << '\n' << "sqrt(2) = " << std::sqrt(2) << '\n' << "golden ratio = " << (1+std::sqrt(5))/2 << '\n'; // special values std::cout << "sqrt(-0) = " << std::sqrt(-0.0) << '\n'; // error handling errno = 0; std::feclearexcept(FE_ALL_EXCEPT); std::cout << "sqrt(-1.0) = " << std::sqrt(-1) << '\n'; if(errno == EDOM) std::cout << " errno = EDOM " << std::strerror(errno) << '\n'; if(std::fetestexcept(FE_INVALID)) std::cout << " FE_INVALID raised\n"; }
Possible output:
sqrt(100) = 10 sqrt(2) = 1.41421 golden ratio = 1.61803 sqrt(-0) = -0 sqrt(-1.0) = -nan errno = EDOM Numerical argument out of domain FE_INVALID raised
See also
raises a number to the given power (xy) (function) | |
(C++11) |
computes cubic root (3√x) (function) |
(C++11) |
computes square root of the sum of the squares of two given numbers (√x2 +y2 ) (function) |
complex square root in the range of the right half-plane (function template) | |
applies the function std::sqrt to each element of valarray (function template) | |
C documentation for sqrt
|