nan(3) Library Functions Manual nan(3) nan, nanf, nanl - <> ( ) LIBRARY Math library (libm, -lm) #include double nan(const char *tagp); float nanf(const char *tagp); long double nanl(const char *tagp); glibc (. feature_test_macros(7)): nan(), nanf(), nanl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L ( tagp) NaN. (quiet) NaN, . nan(" ") : strtod("NAN( )", NULL); nanf() nanl() strtof(3) strtold(3). tagp . , IEEE 754, NaN, tagp . . attributes(7). +----------------------------+----------------------------------------------------------+--------------------------+ | | | | +----------------------------+----------------------------------------------------------+--------------------------+ |nan(), nanf(), nanl() | | MT-Safe locale | +----------------------------+----------------------------------------------------------+--------------------------+ C11, POSIX.1-2008. See also IEC 559 and the appendix with recommended functions in IEEE 754/IEEE 854. glibc 2.1. C99, POSIX.1-2001. . isnan(3), strtod(3), math_error(7) Alex Nik , Azamat Hackimov , Dmitry Bolkhovskikh , Yuri Kozlov ; GNU 3 , . . , , . Linux man-pages 6.06 31 2023 . nan(3)