ECVT(P) POSIX Programmer's Manual ECVT(P)
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-ter-
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
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 dig-
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 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 ECVT(P)