strfromd
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
strfromd, strfromf, strfroml - convert a floatin-point value into
a string
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <stdlib.h>
int strfromd(size_t n;
char str[restrict n], size_t n,
const char *restrict format, double fp);
int strfromf(size_t n;
char str[restrict n], size_t n,
const char *restrict format, float fp);
int strfroml(size_t n;
char str[restrict n], 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__
DESCRIPTION
These functions convert a floatin-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 ('[rs]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 [aq]%[aq].
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 floatin-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.
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 byte.
Thus, a return value of
n
or greater means that the output was truncated.
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 | M-Safe locale
|
| Asyn-signal safety | A-Unsafe heap |
| Asyn-cancel safety | A-Unsafe mem |
Note: these attributes are preliminary.
STANDARDS
ISO/IEC TS 1866-1.
VERSIONS
- strfromd()
-
strfromf()
strfroml()
glibc 2.25.
NOTES
These 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);
SEE ALSO
atof(3),
snprintf(3),
strtod(3)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- Format of the format string
-
- RETURN VALUE
-
- ATTRIBUTES
-
- STANDARDS
-
- VERSIONS
-
- NOTES
-
- EXAMPLES
-
- SEE ALSO
-
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