| .\" Copyright (c) 2016, IBM Corporation. |
| .\" Written by Wainer dos Santos Moschetta <wainersm@linux.vnet.ibm.com> |
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| .\" 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 2021-03-22 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| strfromd, strfromf, strfroml \- convert a floating-point value into |
| a string |
| .SH SYNOPSIS |
| .nf |
| .B #include <stdlib.h> |
| .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 |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR strfromd (), |
| .BR strfromf (), |
| .BR strfroml (): |
| .nf |
| __STDC_WANT_IEC_60559_BFP_EXT__ |
| .fi |
| .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 byte ('\e0') 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 byte. |
| 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 |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR strfromd (), |
| .BR strfromf (), |
| .BR strfroml () |
| T} Thread safety MT-Safe locale |
| \^ Async-signal safety AS-Unsafe heap |
| \^ Async-cancel safety AC-Unsafe mem |
| .TE |
| .hy |
| .ad |
| .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 +4n |
| .EX |
| #define __STDC_WANT_IEC_60559_BFP_EXT__ |
| #include <stdlib.h> |
| 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 +4n |
| .EX |
| #define __STDC_WANT_IEC_60559_BFP_EXT__ |
| #include <stdlib.h> |
| 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 +4n |
| .EX |
| #define __STDC_WANT_IEC_60559_BFP_EXT__ |
| #include <stdlib.h> |
| 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) |