strfromd(3)

1strfromd(3)                Library Functions Manual                strfromd(3)
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NAME

6       strfromd,  strfromf,  strfroml  - convert a floating-point value into a
7       string
8

LIBRARY

10       Standard C library (libc, -lc)
11

SYNOPSIS

13       #include <stdlib.h>
14
15       int strfromd(char str[restrict .n], size_t n,
16                    const char *restrict format, double fp);
17       int strfromf(char str[restrict .n], size_t n,
18                    const char *restrict format, float fp);
19       int strfroml(char str[restrict .n], size_t n,
20                    const char *restrict format, long double fp);
21
22   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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24       strfromd(), strfromf(), strfroml():
25           __STDC_WANT_IEC_60559_BFP_EXT__
26

DESCRIPTION

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

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

74       For an explanation of the terms used in this section, see attributes(7)
75       and the POSIX Safety Concepts section in GNU C Library manual.
76
77       ┌───────────────────────────────┬─────────────────────┬────────────────┐
78       │Interface                      │ Attribute           │ Value          │
79       ├───────────────────────────────┼─────────────────────┼────────────────┤
80       │                               │ Thread safety       │ MT-Safe locale │
81       │strfromd(), strfromf(),        ├─────────────────────┼────────────────┤
82       │strfroml()                     │ Async-signal safety │ AS-Unsafe heap │
83       │                               ├─────────────────────┼────────────────┤
84       │                               │ Async-cancel safety │ AC-Unsafe mem  │
85       └───────────────────────────────┴─────────────────────┴────────────────┘
86       Note: these attributes are preliminary.
87

STANDARDS

89       ISO/IEC TS 18661-1.
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VERSIONS

92       strfromd()
93       strfromf()
94       strfroml()
95              glibc 2.25.
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NOTES

98       These  functions take account of the LC_NUMERIC category of the current
99       locale.
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EXAMPLES

102       To convert the value 12.1 as a float type to  a  string  using  decimal
103       notation, resulting in "12.100000":
104
105           #define __STDC_WANT_IEC_60559_BFP_EXT__
106           #include <stdlib.h>
107           int ssize = 10;
108           char s[ssize];
109           strfromf(s, ssize, "%f", 12.1);
110
111       To  convert the value 12.3456 as a float type to a string using decimal
112       notation with two digits of precision, resulting in "12.35":
113
114           #define __STDC_WANT_IEC_60559_BFP_EXT__
115           #include <stdlib.h>
116           int ssize = 10;
117           char s[ssize];
118           strfromf(s, ssize, "%.2f", 12.3456);
119
120       To convert the value 12.345e19 as a double type to a string using  sci‐
121       entific notation with zero digits of precision, resulting in "1E+20":
122
123           #define __STDC_WANT_IEC_60559_BFP_EXT__
124           #include <stdlib.h>
125           int ssize = 10;
126           char s[ssize];
127           strfromd(s, ssize, "%.E", 12.345e19);
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