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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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STRFROMD(3) Linux Programmer's Manual STRFROMD(3)
strfromd, strfromf, strfroml - convert a floating-point value
into a string
#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);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
strfromd(), strfromf(), strfroml():
__STDC_WANT_IEC_60559_BFP_EXT__
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 byte ('\0') 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 '%'. 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, and f (or a, e, g) is the
conversion specifier, the conversion is to "nan", "nan",
or "-nan", respectively. If F (or A, 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.
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 byte. Thus, a
return value of n or greater means that the output was truncated.
The strfromd(), strfromf(), and strfroml() functions are
available in glibc since version 2.25.
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 │
├────────────┼──────────────────────────────────┼────────────────┤
│ │ Thread safety │ MT-Safe locale │
│strfromd(), ├──────────────────────────────────┼────────────────┤
│strfromf(), │ Asynchronous signal safety │ AS-Unsafe heap │
│strfroml() ├──────────────────────────────────┼────────────────┤
│ │ Asynchronous cancellation safety │ AC-Unsafe mem │
└────────────┴──────────────────────────────────┴────────────────┘
Note: these attributes are preliminary.
C99, ISO/IEC TS 18661-1.
The strfromd(), strfromf(), and strfroml() functions take account
of the LC_NUMERIC category of the current locale.
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);
atof(3), snprintf(3), strtod(3)
This page is part of release 5.10 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/.
GNU 2019-03-06 STRFROMD(3)
Pages that refer to this page: atof(3), printf(3), strtod(3)
Copyright and license for this manual page
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