The ecvt() function converts value to a null-terminated string of ndigit digits (where ndigit is reduced to an unspecified limit determined by the precision of a double) and returns a pointer to the string. The high-order digit is non-zero, unless the value is 0. The low-order digit is rounded. The position of the radix character relative to the beginning of the string is stored in the integer pointed to by decpt (negative means to the left of the returned digits). The radix character is not included in the returned string. If the sign of the result is negative, the integer pointed to by sign is non-zero, otherwise it is 0.

If the converted value is out of range or is not representable, the contents of the returned string are unspecified.

The fcvt() function is identical to ecvt() except that ndigit specifies the number of digits desired after the radix point. The total number of digits in the result string is restricted to an unspecified limit as determined by the precision of a double.

The gcvt() function converts value to a null-terminated string (similar to that of the %g format of printf(3C)) in the array pointed to by buf and returns buf. It produces ndigit significant digits (limited to an unspecified value determined by the precision of a double) in %f if possible, or %e (scientific notation) otherwise. A minus sign is included in the returned string if value is less than 0. A radix character is included in the returned string if value is not a whole number. Trailing zeros are suppressed where value is not a whole number. The radix character is determined by the current locale. If setlocale(3C) has not been called successfully, the default locale, POSIX, is used. The default locale specifies a period (.) as the radix character. The LC_NUMERIC category determines the value of the radix character within the current locale.