sqrt - Man Page

square root function


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <math.h>

double sqrt(double x);
float sqrtf(float x);
long double sqrtl(long double x);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

These functions shall compute the square root of their argument x, x.

An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Return Value

Upon successful completion, these functions shall return the square root of x.

For finite values of x < -0, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.

If x is NaN, a NaN shall be returned.

If x is ±0 or +Inf, x shall be returned.

If x is -Inf, a domain error shall occur, and a NaN shall be returned.


These functions shall fail if:

Domain Error

The finite value of x is < -0, or x is -Inf.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

The following sections are informative.


Taking the Square Root of 9.0

#include <math.h>
double x = 9.0;
double result;
result = sqrt(x);

Application Usage

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.



Future Directions


See Also

feclearexcept(), fetestexcept(), isnan()

The Base Definitions volume of POSIX.1-2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, <math.h>, <stdio.h>

Referenced By

atan2(3p), hypot(3p), math.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual