strfromf(3)

1STRFROMD(3)                Linux Programmer's Manual               STRFROMD(3)
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NAME

6       strfromd,  strfromf,  strfroml  - convert a floating-point value into a
7       string
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SYNOPSIS

10       #include <stdlib.h>
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12       int strfromd(char *restrict str, size_t n,
13                    const char *restrict format, double fp);
14       int strfromf(char *restrict str, size_t n,
15                    const char *restrict format, float fp);
16       int strfroml(char *restrict str, size_t n,
17                    const char *restrict format, long double fp);
18
19   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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21       strfromd(), strfromf(), strfroml():
22           __STDC_WANT_IEC_60559_BFP_EXT__
23

DESCRIPTION

25       These functions convert a floating-point value, fp, into  a  string  of
26       characters,  str, with a configurable format string.  At most n charac‐
27       ters are stored into str.
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29       The terminating null byte ('\0') is written if and only if n is  suffi‐
30       ciently  large,  otherwise the written string is truncated at n charac‐
31       ters.
32
33       The strfromd(), strfromf(), and strfroml() functions are equivalent to
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35           snprintf(str, n, format, fp);
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37       except for the format string.
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39   Format of the format string
40       The format string must start with the character '%'.  This is  followed
41       by  an  optional  precision which starts with the period character (.),
42       followed by an optional decimal integer.  If no  integer  is  specified
43       after  the period character, a precision of zero is used.  Finally, the
44       format string should have one of the conversion specifiers a, A, e,  E,
45       f, F, g, or G.
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47       The  conversion  specifier  is applied based on the floating-point type
48       indicated by the function suffix.  Therefore,  unlike  snprintf(),  the
49       format   string  does  not  have  a  length  modifier  character.   See
50       snprintf(3) for a detailed description of these conversion specifiers.
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52       The implementation conforms to the C99 standard on  conversion  of  NaN
53       and infinity values:
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55              If fp is a NaN, +NaN, or -NaN, and f (or a, e, g) is the conver‐
56              sion specifier, the conversion is to "nan",  "nan",  or  "-nan",
57              respectively.   If  F  (or A, E, G) is the conversion specifier,
58              the conversion is to "NAN" or "-NAN".
59
60              Likewise if fp is infinity, it is converted to [-]inf or [-]INF.
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62       A malformed format string results in undefined behavior.
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RETURN VALUE

65       The strfromd(), strfromf(), and strfroml() functions return the  number
66       of  characters  that  would  have  been  written in str if n had enough
67       space, not counting the terminating null byte.  Thus, a return value of
68       n or greater means that the output was truncated.
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VERSIONS

71       The  strfromd(),  strfromf(), and strfroml() functions are available in
72       glibc since version 2.25.
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ATTRIBUTES

75       For an explanation of the terms used in this section, see attributes(7)
76       and the POSIX Safety Concepts section in GNU C Library manual.
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78       ┌────────────┬──────────────────────────────────┬────────────────┐
79       │Interface   │ Attribute                        │ Value          │
80       ├────────────┼──────────────────────────────────┼────────────────┤
81       │            │ Thread safety                    │ MT-Safe locale │
82       │strfromd(), ├──────────────────────────────────┼────────────────┤
83       │strfromf(), │ Asynchronous signal safety       │ AS-Unsafe heap │
84       │strfroml()  ├──────────────────────────────────┼────────────────┤
85       │            │ Asynchronous cancellation safety │ AC-Unsafe mem  │
86       └────────────┴──────────────────────────────────┴────────────────┘
87       Note: these attributes are preliminary.
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CONFORMING TO

90       C99, ISO/IEC TS 18661-1.
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NOTES

93       The  strfromd(),  strfromf(),  and strfroml() functions take account of
94       the LC_NUMERIC category of the current locale.
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EXAMPLES

97       To convert the value 12.1 as a float type to a string using decimal no‐
98       tation, resulting in "12.100000":
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100           #define __STDC_WANT_IEC_60559_BFP_EXT__
101           #include <stdlib.h>
102           int ssize = 10;
103           char s[ssize];
104           strfromf(s, ssize, "%f", 12.1);
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106       To  convert the value 12.3456 as a float type to a string using decimal
107       notation with two digits of precision, resulting in "12.35":
108
109           #define __STDC_WANT_IEC_60559_BFP_EXT__
110           #include <stdlib.h>
111           int ssize = 10;
112           char s[ssize];
113           strfromf(s, ssize, "%.2f", 12.3456);
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115       To convert the value 12.345e19 as a double type to a string using  sci‐
116       entific notation with zero digits of precision, resulting in "1E+20":
117
118           #define __STDC_WANT_IEC_60559_BFP_EXT__
119           #include <stdlib.h>
120           int ssize = 10;
121           char s[ssize];
122           strfromd(s, ssize, "%.E", 12.345e19);
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COLOPHON

128       This  page  is  part of release 5.10 of the Linux man-pages project.  A
129       description of the project, information about reporting bugs,  and  the
130       latest     version     of     this    page,    can    be    found    at
131       https://www.kernel.org/doc/man-pages/.
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135GNU                               2019-03-06                       STRFROMD(3)