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SYNOPSIS top

#include <stdlib.h>int strfromd(size_t n;charstr[restrictn], size_tn,const char *restrictformat, doublefp);int strfromf(size_t n;charstr[restrictn], size_tn,const char *restrictformat, floatfp);int strfroml(size_t n;charstr[restrictn], size_tn,const char *restrictformat, long doublefp); Feature Test Macro Requirements for glibc (seefeature_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 configurableformat string. At mostn characters are stored intostr. The terminating null byte ('\0') is written if and only ifn is sufficiently large, otherwise the written string is truncated atn characters. Thestrfromd(),strfromf(), andstrfroml() functions are equivalent to snprintf(str, n, format, fp); except for theformat string.Format of the format string Theformat 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 specifiersa,A,e,E,f,F,g, orG. The conversion specifier is applied based on the floating-point type indicated by the function suffix. Therefore, unlikesnprintf(), the format string does not have a length modifier character. Seesnprintf(3) for a detailed description of these conversion specifiers. The implementation conforms to the C99 standard on conversion of NaN and infinity values: Iffp is a NaN, +NaN, or -NaN, andf(ora,e,g) is the conversion specifier, the conversion is to "nan", "nan", or "-nan", respectively. IfF(orA,E,G) is the conversion specifier, the conversion is to "NAN" or "-NAN". Likewise iffp is infinity, it is converted to [-]inf or [-]INF. A malformedformat string results in undefined behavior.

Thestrfromd(),strfromf(), andstrfroml() functions return the number of characters that would have been written instr ifn had enough space, not counting the terminating null byte. Thus, a return value ofn or greater means that the output was truncated.

ATTRIBUTES top

For an explanation of the terms used in this section, seeattributes(7) and thePOSIX Safety Conceptssection 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.

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);

COLOPHON top

This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-06-28strfromd(3)

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