man3/ecvt.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" References consulted:
   6 .\"     Linux libc source code
   7 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
   8 .\"     386BSD man pages
   9 .\" Modified Sat Jul 24 19:40:39 1993 by Rik Faith (faith@cs.unc.edu)
  10 .\" Modified Fri Jun 25 12:10:47 1999 by Andries Brouwer (aeb@cwi.nl)
  11 .\"
  12 .TH ECVT 3 2021-03-22 GNU "Linux Programmer's Manual"
  13 .SH NAME
  14 ecvt, fcvt \- convert a floating-point number to a string
  15 .SH LIBRARY
  16 Standard C library
  17 .RI ( libc ", " \-lc )
  18 .SH SYNOPSIS
  19 .nf
  20 .B #include <stdlib.h>
  21 .PP
  22 .BI "char *ecvt(double " number ", int " ndigits ", int *restrict " decpt ,
  23 .BI "           int *restrict " sign );
  24 .BI "char *fcvt(double " number ", int " ndigits ", int *restrict " decpt ,
  25 .BI "           int *restrict " sign );
  26 .fi
  27 .PP
  28 .RS -4
  29 Feature Test Macro Requirements for glibc (see
  30 .BR feature_test_macros (7)):
  31 .RE
  32 .PP
  33 .BR ecvt (),
  34 .BR fcvt ():
  35 .nf
  36     Since glibc 2.17
  37         (_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200809L))
  38             || /* Glibc >= 2.20 */ _DEFAULT_SOURCE
  39             || /* Glibc <= 2.19 */ _SVID_SOURCE
  40     Glibc versions 2.12 to 2.16:
  41         (_XOPEN_SOURCE >= 500 && ! (_POSIX_C_SOURCE >= 200112L))
  42             || _SVID_SOURCE
  43     Before glibc 2.12:
  44         _SVID_SOURCE || _XOPEN_SOURCE >= 500
  45 .\"        || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  46 .fi
  47 .SH DESCRIPTION
  48 The
  49 .BR ecvt ()
  50 function converts \fInumber\fP to a null-terminated
  51 string of \fIndigits\fP digits (where \fIndigits\fP is reduced to a
  52 system-specific limit determined by the precision of a
  53 .IR double ),
  54 and returns a pointer to the string.
  55 The high-order digit is nonzero, unless
  56 .I number
  57 is zero.
  58 The low order digit is rounded.
  59 The string itself does not contain a decimal point; however,
  60 the position of the decimal point relative to the start of the string
  61 is stored in \fI*decpt\fP.
  62 A negative value for \fI*decpt\fP means that
  63 the decimal point is to the left of the start of the string.
  64 If the sign of
  65 \fInumber\fP is negative, \fI*sign\fP is set to a nonzero value,
  66 otherwise it is set to 0.
  67 If
  68 .I number
  69 is zero, it is unspecified whether \fI*decpt\fP is 0 or 1.
  70 .PP
  71 The
  72 .BR fcvt ()
  73 function is identical to
  74 .BR ecvt (),
  75 except that
  76 \fIndigits\fP specifies the number of digits after the decimal point.
  77 .SH RETURN VALUE
  78 Both the
  79 .BR ecvt ()
  80 and
  81 .BR fcvt ()
  82 functions return a pointer to a
  83 static string containing the ASCII representation of \fInumber\fP.
  84 The static string is overwritten by each call to
  85 .BR ecvt ()
  86 or
  87 .BR fcvt ().
  88 .SH ATTRIBUTES
  89 For an explanation of the terms used in this section, see
  90 .BR attributes (7).
  91 .ad l
  92 .nh
  93 .TS
  94 allbox;
  95 lbx lb lb
  96 l l l.
  97 Interface       Attribute       Value
  98 T{
  99 .BR ecvt ()
 100 T}      Thread safety   MT-Unsafe race:ecvt
 101 T{
 102 .BR fcvt ()
 103 T}      Thread safety   MT-Unsafe race:fcvt
 104 .TE
 105 .hy
 106 .ad
 107 .sp 1
 108 .SH CONFORMING TO
 109 SVr2;
 110 marked as LEGACY in POSIX.1-2001.
 111 POSIX.1-2008 removes the specifications of
 112 .BR ecvt ()
 113 and
 114 .BR fcvt (),
 115 recommending the use of
 116 .BR sprintf (3)
 117 instead (though
 118 .BR snprintf (3)
 119 may be preferable).
 120 .SH NOTES
 121 .\" Linux libc4 and libc5 specified the type of
 122 .\" .I ndigits
 123 .\" as
 124 .\" .IR size_t .
 125 Not all locales use a point as the radix character ("decimal point").
 126 .SH SEE ALSO
 127 .BR ecvt_r (3),
 128 .BR gcvt (3),
 129 .BR qecvt (3),
 130 .BR setlocale (3),
 131 .BR sprintf (3)