The ecvt(), fcvt(), and gcvt() functions shall convert
floating-point numbers to null-terminated strings.
The ecvt() function shall convert 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 return a
pointer to the string. The high-order digit shall be non-zero, unless the
value is 0. The low-order digit shall be rounded in an implementation-defined
manner. The position of the radix character relative to the beginning of the
string shall be stored in the integer pointed to by decpt (negative
means to the left of the returned digits). If value is zero, it is
unspecified whether the integer pointed to by decpt would be 0 or 1.
The radix character shall not be included in the returned string. If the sign
of the result is negative, the integer pointed to by sign shall be
non-zero; otherwise, it shall be 0.
If the converted value is out of range or is not representable, the contents of
the returned string are unspecified.
The fcvt() function shall be equivalent to ecvt(), except that
ndigit specifies the number of digits desired after the radix
character. 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 shall convert value to a null-terminated
string (similar to that of the %g conversion specification format of
printf()) in the array pointed to by buf and shall return
buf. It shall produce ndigit significant digits (limited to an
unspecified value determined by the precision of a double) in the
%f conversion specification format of printf() if possible, or
the %e conversion specification format of printf() (scientific
notation) otherwise. A minus sign shall be included in the returned string if
value is less than 0. A radix character shall be included in the
returned string if value is not a whole number. Trailing zeros shall be
suppressed where value is not a whole number. The radix character is
determined by the current locale. If setlocale() 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.
These functions need not be reentrant. A function that is not required to be
reentrant is not required to be thread-safe.
The ecvt() and fcvt() functions shall return a pointer to a
null-terminated string of digits.
The gcvt() function shall return buf.
The return values from ecvt() and fcvt() may point to static data
which may be overwritten by subsequent calls to these functions.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html