gcvt
(3)convert a floating-point number to a string
#include <stdlib.h> char *gcvt(double number, int ndigit, char *buf); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): gcvt(): Since glibc 2.17 (_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200809L)) || /* glibc >= 2.20 */ _DEFAULT_SOURCE || /* glibc <= 2.19 */ _SVID_SOURCE glibc 2.12 to glibc 2.16: (_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200112L)) || _SVID_SOURCE Before glibc 2.12: _SVID_SOURCE || _XOPEN_SOURCE >= 500