man3/ecvt.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  12 .\" Since the Linux kernel and libraries are constantly changing, this
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  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Sat Jul 24 19:40:39 1993 by Rik Faith (faith@cs.unc.edu)
  28 .\" Modified Fri Jun 25 12:10:47 1999 by Andries Brouwer (aeb@cwi.nl)
  29 .\"
  30 .TH ECVT 3 2010-09-20 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 ecvt, fcvt \- convert a floating-point number to a string
  33 .SH SYNOPSIS
  34 .B #include <stdlib.h>
  35 .sp
  36 .BI "char *ecvt(double " number ", int " ndigits ", int *" decpt ,
  37 .BI "int *" sign );
  38 .sp
  39 .BI "char *fcvt(double " number ", int " ndigits ", int *" decpt ,
  40 .BI "int *" sign );
  41 .sp
  42 .in -4n
  43 Feature Test Macro Requirements for glibc (see
  44 .BR feature_test_macros (7)):
  45 .in
  46 .sp
  47 .BR ecvt (),
  48 .BR fcvt ():
  49 .ad l
  50 .RS 4
  51 .PD 0
  52 .TP 4
  53 Since glibc 2.12:
  54 .nf
  55 _SVID_SOURCE ||
  56     (_XOPEN_SOURCE\ >=\ 500 ||
  57         _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
  58     !(_POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600)
  59 .fi
  60 .TP 4
  61 Before glibc 2.12:
  62 _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  63 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  64 .PD
  65 .RE
  66 .ad b
  67 .SH DESCRIPTION
  68 The
  69 .BR ecvt ()
  70 function converts \fInumber\fP to a null-terminated
  71 string of \fIndigits\fP digits (where \fIndigits\fP is reduced to a
  72 system-specific limit determined by the precision of a
  73 .IR double ),
  74 and returns a pointer to the string.
  75 The high-order digit is nonzero, unless
  76 .I number
  77 is zero.
  78 The low order digit is rounded.
  79 The string itself does not contain a decimal point; however,
  80 the position of the decimal point relative to the start of the string
  81 is stored in \fI*decpt\fP.
  82 A negative value for \fI*decpt\fP means that
  83 the decimal point is to the left of the start of the string.
  84 If the sign of
  85 \fInumber\fP is negative, \fI*sign\fP is set to a nonzero value,
  86 otherwise it is set to 0.
  87 If
  88 .I number
  89 is zero, it is unspecified whether \fI*decpt\fP is 0 or 1.
  90 .PP
  91 The
  92 .BR fcvt ()
  93 function is identical to
  94 .BR ecvt (),
  95 except that
  96 \fIndigits\fP specifies the number of digits after the decimal point.
  97 .SH RETURN VALUE
  98 Both the
  99 .BR ecvt ()
 100 and
 101 .BR fcvt ()
 102 functions return a pointer to a
 103 static string containing the ASCII representation of \fInumber\fP.
 104 The static string is overwritten by each call to
 105 .BR ecvt ()
 106 or
 107 .BR fcvt ().
 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)