COS(3P) POSIX Programmer's Manual COS(3P)PROLOG
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.
cos, cosf, cosl — cosine function
double cos(double x);
float cosf(float x);
long double cosl(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.1‐2008
defers to the ISO C standard.
These functions shall compute the cosine of their argument x, measured
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
Upon successful completion, these functions shall return the cosine of
If x is NaN, a NaN shall be returned.
If x is ±0, the value 1.0 shall be returned.
If x is ±Inf, a domain error shall occur, and a NaN shall be returned.
These functions shall fail if:
The x argument 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
The following sections are informative.
Taking the Cosine of a 45-Degree Angle
double radians = 45 * M_PI / 180;
result = cos(radians);
These functions may lose accuracy when their argument is near an odd
multiple of π/2 or is far from 0.
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.
SEE ALSOacos(), feclearexcept(), fetestexcept(), isnan(), sin(), tan()
The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
Error Conditions for Mathematical Functions, <math.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
IEEE/The Open Group 2013 COS(3P)