Section (3) strfromd
Name
strfromd, strfromf, strfroml — convert a floating-point value into a string
Synopsis
#include <stdlib.h>
int
strfromd( |
char *restrict str, |
size_t n, | |
const char *restrict format, | |
double fp) ; |
int
strfromf( |
char *restrict str, |
size_t n, | |
const char *restrict format, | |
float fp) ; |
int
strfroml( |
char *restrict str, |
size_t n, | |
const char *restrict format, | |
long double fp) ; |
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Note | ||
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DESCRIPTION
These functions convert a floating-point value, fp
, into a string of
characters, str
, with
a configurable format
string. At most n
characters are stored into str
.
The terminating null character (_zsingle_quotesz_ _zsingle_quotesz_) is written if and
only if n
is
sufficiently large, otherwise the written string is truncated
at n
characters.
The strfromd
(), strfromf
(), and strfroml
() functions are equivalent to
snprintf(str, n, format, fp);
except for the format
string.
Format of the format string
The format
string must start with the character _zsingle_quotesz_%_zsingle_quotesz_. This is followed
by an optional precision which starts with the period
character (.), followed by an optional decimal integer. If
no integer is specified after the period character, a
precision of zero is used. Finally, the format string
should have one of the conversion specifiers a
, A
,
e
, E
, f
,
F
, g
, or G
.
The conversion specifier is applied based on the
floating-point type indicated by the function suffix.
Therefore, unlike snprintf
(),
the format string does not have a length modifier
character. See snprintf(3) for a
detailed description of these conversion specifiers.
The implementation conforms to the C99 standard on conversion of NaN and infinity values:
If
fp
is a NaN, +NaN, or -NaN, andf
(ora
,e
,g
) is the conversion specifier, the conversion is to nan, nan, or -nan, respectively. IfF
(orA
,E
,G
) is the conversion specifier, the conversion is to NAN or -NAN.Likewise if
fp
is infinity, it is converted to [-]inf or [-]INF.
A malformed format
string results in
undefined behavior.
RETURN VALUE
The strfromd
(), strfromf
(), and strfroml
() functions return the number of
characters that would have been written in str
if n
had enough space, not
counting the terminating null character. Thus, a return value
of n
or greater means
that the output was truncated.
VERSIONS
The strfromd
(), strfromf
(), and strfroml
() functions are available in glibc
since version 2.25.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7) and the POSIX Safety Concepts section in GNU C Library manual.
Interface | Attribute | Value |
strfromd (), strfromf (), strfroml () |
Thread safety | MT-Safe locale |
Asynchronous signal safety | AS-Unsafe heap | |
Asynchronous cancellation safety | AC-Unsafe mem |
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Note |
---|---|
These attributes are preliminary. |
NOTES
The strfromd
(), strfromf
(), and strfroml
() functions take account of the
LC_NUMERIC
category of the
current locale.
EXAMPLES
To convert the value 12.1 as a float type to a string using decimal notation, resulting in 12.100000:
#define __STDC_WANT_IEC_60559_BFP_EXT__ #include <stdlib.h> int ssize = 10; char s[ssize]; strfromf(s, ssize, %f, 12.1);
To convert the value 12.3456 as a float type to a string using decimal notation with two digits of precision, resulting in 12.35:
#define __STDC_WANT_IEC_60559_BFP_EXT__ #include <stdlib.h> int ssize = 10; char s[ssize]; strfromf(s, ssize, %.2f, 12.3456);
To convert the value 12.345e19 as a double type to a string using scientific notation with zero digits of precision, resulting in 1E+20:
#define __STDC_WANT_IEC_60559_BFP_EXT__ #include <stdlib.h> int ssize = 10; char s[ssize]; strfromd(s, ssize, %.E, 12.345e19);
COLOPHON
This page is part of release 5.04 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (c) 2016, IBM Corporation. Written by Wainer dos Santos Moschetta <wainersmlinux.vnet.ibm.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume. no responsibility for errors or omissions, or for damages resulting. from the use of the information contained herein. The author(s) may. not have taken the same level of care in the production of this. manual, which is licensed free of charge, as they might when working. professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END References consulted: Glibc 2.25 source code and manual. C99 standard document. ISO/IEC TS 18661-1 technical specification. snprintf and other man.3 pages. |