strfromd

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



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);

   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 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.

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.

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          │
       ├─────────────────────────────────┼─────────────────────┼────────────────┤
       │                                 │ Thread safety       │ MT-Safe locale │
       │strfromd(), strfromf(),          ├─────────────────────┼────────────────┤
       │strfroml()                       │ Async-signal safety │ AS-Unsafe heap │
       │                                 ├─────────────────────┼────────────────┤
       │                                 │ Async-cancel safety │ AC-Unsafe mem  │
       └─────────────────────────────────┴─────────────────────┴────────────────┘
       Note: these attributes are preliminary.

CONFORMING TO
       C99, ISO/IEC TS 18661-1.

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);

SEE ALSO
       atof(3), snprintf(3), strtod(3)

COLOPHON
       This page is part of release 5.13 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                                2021-03-22                        STRFROMD(3)