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 character ('\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
       character.  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

       This page is part of release 4.15 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/.