Linux Programmer’s Manual
copysign, copysignf, copysignl − copy sign of a number
double copysign(double x, double y);
float copysignf(float x, float y);
long double copysignl(long double x, long double y);
Link with −lm.
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
copysign(), copysignf(), copysignl(): _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 600
|| _ISOC99_SOURCE; or cc -std=c99
The copysign() functions return a value whose absolute value matches that of x, but whose sign bit matches
that of y.
On success, these functions return a value whose magnitude is taken from x and whose sign is taken from
If x is a NaN, a NaN with the sign bit of y is returned.
No errors occur.
C99, POSIX.1-2001. This function is defined in IEC 559 (and the appendix with recommended functions
in IEEE 754/IEEE 854).
On architectures where the floating-point formats are not IEEE 754 compliant, the copysign() functions
may treat a negative zero as positive.
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