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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 charac-
     ters 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 conver-
            sion  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  sci-
     entific 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);