NAME

sqrt, sqrtf, sqrtl — square root function

SYNOPSIS

#include <math.h>

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


DESCRIPTION

^[CX] 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.1-2024 defers to the ISO C standard.

These functions shall compute the square root of their argument \(x\), \(\sqrt{x}\).

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 \(x\).

^[MX] The returned value shall be dependent on the current rounding direction mode.

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

^[MX] 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.

ERRORS

These functions shall fail if:

Domain Error

The finite value of \(x\) is < -0, ^[MX]  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.

EXAMPLES

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.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

feclearexcept, fetestexcept, isnan

XBD 4.23 Treatment of Error Conditions for Mathematical Functions, <math.h>, <stdio.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

Issue 6

The sqrtf() and sqrtl() functions are added for alignment with the ISO/IEC 9899:1999 standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0588 [320] is applied.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.