#include <stdlib.h>
int ecvt_r(double number, int ndigits, int *decpt,
int *sign, char *buf, size_t len);
int fcvt_r(double number, int ndigits, int *decpt,
int *sign, char *buf, size_t len);
int qecvt_r(long double number, int ndigits, int *decpt,
int *sign, char *buf, size_t len);
int qfcvt_r(long double number, int ndigits, int *decpt,
int *sign, char *buf, size_t len);
glibc 向けの機能検査マクロの要件 (feature_test_macros(7) 参照):
ecvt_r(), fcvt_r(), qecvt_r(), qfcvt_r(): _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500