finite(3) Library Functions Manual finite(3) finite finitef finitel isinf isinff isinfl isnan isnanf isnanl - (floating-point) BSD (libm -lm) #include int finite(double x); int finitef(float x); int finitel(long double x); int isinf(double x); int isinff(float x); int isinfl(long double x); int isnan(double x); int isnanf(float x); int isnanl(long double x); glibc ( feature_test_macros(7)): finite(), finitef(), finitel(): /* glibc >= 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE isinf(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || /* glibc >= 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE isinff(), isinfl(): /* glibc >= 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE isnan(): _XOPEN_SOURCE || _ISOC99_SOURCE || /* glibc >= 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE isnanf(), isnanl(): _XOPEN_SOURCE >= 600 || /* glibc >= 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE finite() finitef() finitel() x " " (NaN) 0 . isnan() isnanf() isnanl() x NaN 0 . isinf() isinff() isinfl() 1 x -1 x 0 . attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |finite() | | MT-Safe | |finitef()| | | |finitel()| | | |isinf() | | | |isinff() | | | |isinfl() | | | |isnan() | | | |isnanf() | | | |isnanl() | | | +------------+------------------------------------+--------------------+ . C99 isfinite() isinf() isnan() ( ) . isinf() C99 . fpclassify(3). fpclassify(3) 3 . . : . 6.18 8 2026 finite(3)