ECVT(3P) POSIX Programmer's Manual ECVT(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
ecvt, fcvt, gcvt - convert a floating-point number to a string (LEGACY)
char *ecvt(double value, int ndigit, int *restrict decpt,
int *restrict sign);
char *fcvt(double value, int ndigit, int *restrict decpt,
int *restrict sign);
char *gcvt(double value, int ndigit, char *buf);
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 charac-
ter 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.
No errors are defined.
The following sections are informative.
The sprintf() function is preferred over this function.
These functions may be withdrawn in a future version.
printf(), setlocale(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- 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 .
/The Open Group 2003 ECVT(3P)