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(), │ Asynchronous signal safety       │ AS-Unsafe heap │
       │strfroml()  ├──────────────────────────────────┼────────────────┤
       │            │ Asynchronous cancellation 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

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