strfromd(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

       #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         top

       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         top

       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         top

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

ATTRIBUTES         top

       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         top

       C99, ISO/IEC TS 18661-1.

NOTES         top

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

EXAMPLES         top

       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         top

       atof(3), snprintf(3), strtod(3)

COLOPHON         top

       This page is part of release 5.11 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)

Pages that refer to this page: atof(3)printf(3)strtod(3)