.\" Copyright (c) 2016, IBM Corporation. .\" Written by Wainer dos Santos Moschetta .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of .\" this manual under the conditions for verbatim copying, provided that .\" the entire resulting derived work is distributed under the terms of .\" a permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume. .\" no responsibility for errors or omissions, or for damages resulting. .\" from the use of the information contained herein. The author(s) may. .\" not have taken the same level of care in the production of this. .\" manual, which is licensed free of charge, as they might when working. .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" References consulted: .\" Glibc 2.25 source code and manual. .\" C99 standard document. .\" ISO/IEC TS 18661-1 technical specification. .\" snprintf and other man.3 pages. .\" .TH STRFROMD 3 2017-09-15 "GNU" "Linux Programmer's Manual" .SH NAME strfromd, strfromf, strfroml \- convert a floating-point value into a string .SH SYNOPSIS .nf .B #include .PP .BI "int strfromd(char *restrict " str ", size_t " n ", .BI " const char *restrict " format ", double " fp ");" .BI "int strfromf(char *restrict " str ", size_t " n ", .BI " const char *restrict " format ", float "fp ");" .BI "int strfroml(char *restrict " str ", size_t " n ", .BI " const char *restrict " format ", long double " fp ");" .fi .PP .in -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .PP .ad l .BR strfromd (), .BR strfromf (), .BR strfroml (): .RS 4 __STDC_WANT_IEC_60559_BFP_EXT__ .RE .ad b .SH DESCRIPTION These functions convert a floating-point value, .IR fp , into a string of characters, .IR str , with a configurable .IR format string. At most .I n characters are stored into .IR str . .PP The terminating null character ('\\0') is written if and only if .I n is sufficiently large, otherwise the written string is truncated at .I n characters. .PP The .BR strfromd (), .BR strfromf (), and .BR strfroml () functions are equivalent to .PP .in +4n .EX snprintf(str, n, format, fp); .EE .in .PP except for the .I format string. .SS Format of the format string The .I format string must start with the character \(aq%\(aq. 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 .BR a , .BR A , .BR e , .BR E , .BR f , .BR F , .BR g , or .BR G . .PP The conversion specifier is applied based on the floating-point type indicated by the function suffix. Therefore, unlike .BR snprintf (), the format string does not have a length modifier character. See .BR snprintf (3) for a detailed description of these conversion specifiers. .PP The implementation conforms to the C99 standard on conversion of NaN and infinity values: .PP .RS If .I fp is a NaN, +NaN, or -NaN, and .BR f (or .BR a , .BR e , .BR g ) is the conversion specifier, the conversion is to "nan", "nan", or "-nan", respectively. If .B F (or .BR A , .BR E , .BR G ) is the conversion specifier, the conversion is to "NAN" or "-NAN". .PP Likewise if .I fp is infinity, it is converted to [-]inf or [-]INF. .RE .PP A malformed .I format string results in undefined behavior. .SH RETURN VALUE The .BR strfromd (), .BR strfromf (), and .BR strfroml () functions return the number of characters that would have been written in .I str if .I n had enough space, not counting the terminating null character. Thus, a return value of .I n or greater means that the output was truncated. .SH VERSIONS The .BR strfromd (), .BR strfromf (), and .BR strfroml () functions are available in glibc since version 2.25. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7) and the .B POSIX Safety Concepts section in GNU C Library manual. .PP .TS allbox; lbw11 lb lb l l l. Interface Attribute Value T{ .BR strfromd (), .BR strfromf (), .BR strfroml () T} Thread safety MT-Safe locale \^ Asynchronous signal safety AS-Unsafe heap \^ Asynchronous cancellation safety AC-Unsafe mem .TE .sp 1 Note: these attributes are preliminary. .SH CONFORMING TO C99, ISO/IEC TS 18661-1. .SH NOTES The .BR strfromd (), .BR strfromf (), and .BR strfroml () functions take account of the .B LC_NUMERIC category of the current locale. .SH EXAMPLES To convert the value 12.1 as a float type to a string using decimal notation, resulting in "12.100000": .PP .in +4 .EX #define __STDC_WANT_IEC_60559_BFP_EXT__ #include int ssize = 10; char s[ssize]; strfromf(s, ssize, "%f", 12.1); .EE .in .PP 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": .PP .in +4 .EX #define __STDC_WANT_IEC_60559_BFP_EXT__ #include int ssize = 10; char s[ssize]; strfromf(s, ssize, "%.2f", 12.3456); .EE .in .PP 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": .PP .in +4 .EX #define __STDC_WANT_IEC_60559_BFP_EXT__ #include int ssize = 10; char s[ssize]; strfromd(s, ssize, "%.E", 12.345e19); .EE .in .SH SEE ALSO .BR atof (3), .BR snprintf (3), .BR strtod (3) .SH COLOPHON This page is part of release 4.16 of the Linux .I 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/.