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 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

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