strfromf(3) Linux Man Page - System Grab Bag

Name

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

Library

Standard C library ( libc ", " -lc )

Synopsis

#include <stdlib.h> 
int strfromd(char " str "[restrict ." n "], size_t  n ,
             const char *restrict " format ", double " fp ");
int strfromf(char " str "[restrict ." n "], size_t  n ,
             const char *restrict " format ", float "fp ");
int strfroml(char " str "[restrict ." n "], 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 ('\e0') 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.

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.

allbox; lbx lb lb T{ strfromd()strfromf()strfroml()

Interface	Attribute	Value
T}	Thread safety	MT-Safe locale
\^	Async-signal safety	AS-Unsafe heap
\^	Async-cancel safety	AC-Unsafe mem

Note: these attributes are preliminary.

Standards

ISO/IEC TS 18661-1.

Versions

strfromd() strfromf() strfroml() glibc 2.25.

Notes

These 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);