cacos(), cacosf(), cacosl()

Updated: October 26, 2022

Compute the complex arc cosine


#include <complex.h>

double complex cacos( double complex z );

float complex cacosf( float complex z );

long double complex cacosl( long double complex z );


The value that you want to get the complex arc cosine of.


The general-purpose math library.
(QNX Neutrino 7.1 or later) A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.

Your system requirements will determine how you should work with these libraries:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.


These functions compute the complex arc cosine of z, with branch cuts outside the interval [−1, +1] along the real axis.

To check for error situations, use feclearexcept() and fetestexcept(). For example:


The complex arc cosine of z, in the range [0; Inf) along the real axis and in the range [−iπ; iπ] along the imaginary axis.

If z is: These functions return: Errors:
±0 + 0i π/2 - 0i
±0 - 0i π/2 + 0i
±0 + NaNi π/2 + NaNi
x + Infi, for any finite x π/2 - Infi
x + NaNi, for any nonzero finite x NaN + NaNi
-Inf + yi, for any positive finite y π - Infi
-Inf - yi, for any positive finite y π + Infi
Inf + yi, for any positive finite y 0 - Infi
Inf - yi, for any negative finite y 0 + Infi
-Inf + Infi 3π/4 - Infi
Inf + Infi π/4 - Infi
±Inf + NaNi NaN ± Infi, where the sign of the imaginary part is unspecified
NaN + yi, for any finite y NaN + NaNi
NaN + Infi NaN - Infi
NaN - Infi NaN + Infi
NaN ± NaNi NaN + NaNi

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.


C11, POSIX 1003.1

Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes