qecvt, qfcvt, qgcvt - convert a floating-point number to a string
#include <stdlib.h>
char *qecvt(long double number
, int ndigits
, int *decpt
, int *sign
);
char *qfcvt(long double number
, int ndigits
, int *decpt
, int *sign
);
char *qgcvt(long double number
, int ndigit
, char *buf
);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):