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Encoder/Decoder (UTF-8 Unicode4.0) FILE Functions
Member #1,090
July 2003

I needed the possibility to store Unicode strings for my current project, so i've written some functions that do so using UTF-8.
(Thanks again to Evert and Kirr for suggesting to go for UTF-8 instead of UTF-16.)
Since these functions are not directly dependent of said project, i decided to seperate them and after that, i thought they might be generally useful not only to me, so i present them here free to everyone who wants to use them.:)
C++ hpp,cpp pair is attached.

Header is here, so you don't need to download to see, what it can|can not do:

2 --- Projectname: Encoder/Decoder (UTF-8 Unicode4.0) FILE Functions ---
3 (Targetsystem: Crossplatform)
5 Author: Dennis Busch (
7 Content:
8 Functions for storing and restoring full lines of
9 UTF-8(as described in "Unicode4.0.0 Chapter 3.9") encoded UNICODE
10 'string's , 'wstring's and 'uistring's to and from 'FILE's.
12 Details:
13 Unicode characters that can not be held in a single
14 'memory cell' of the desired target string type will be read but ignored.
16 Footnote1:
17 "The definition of UTF-8 prohibits encoding character numbers between
18 U+D800 and U+DFFF"
19 So characters decoded into that range will be ignored as well and more
20 important, characters from that range will not be encoded on storing.
22 Footnote2:
23 On storing, the ByteOrderMark(BOM) U+FEFF
24 will be stored like any other character encoded in UTF-8,
25 always leading to the octet sequence EF BB BF.
26 On restoring, any sequence decoded to U+FEFF will be ignored, that is
27 it gets not appended to the resulting string.
29 Footnote3:
30 The standard allows only unicodes of a maximum of 21
31 bits to be encoded or decoded. Even though characters
32 with the full range of 32bits *could* be stored in UTF-8
33 using up to 6 octets, this implementation does *NOT* do so.
34 It only correctly encodes, decodes up to 4 octets, as defined by said
35 standard("Unicode4.0.0 Chapter 3.9" UTF-8).
36 Quote: "Unicode4.0.0 Appendix C.3"
37 "those five- and six-byte sequences are illegal for the use
38 of UTF-8 as an encoding form of Unicode characters."
40 Footnote4:
41 This implementation also tries to protect against decoding of invalid
42 octet sequences.
43 It does so by silently reading any invalid sequences, but every such
44 invalid sequence(as it should not be allowed in the first place) will
45 be skipped and an ASCII '?' is given out as result character.
48#include <cstdio>
49#include <cstdlib>
50#include <string>
51using namespace std;
53#if !defined(__DB_utf_eight_HEAD_INCLUDED)
54#define __DB_utf_eight_HEAD_INCLUDED
56/* - All functions return a negative value on failure or if the result
57 would be empty.
58 - The FILE parameter is always expected to be a valid
59 file pointer and it must be opened in binary mode. */
62/* Explicitly Writing the UTF-8 ByteOrderMark
63 (use only once at begin of file) as a signature for external editors */
64int write_bom_utf8(FILE *out);
66// Encoding and Decoding a single UNICODE character to and from file
67int encode_utf8(FILE *out, unsigned int code);
68int decode_utf8(FILE *in, unsigned int *result);
70// Reading string and wstring from file
71/* Starts reading actual character data after ignoring any preceeding newline
72 or carriage return codes or byte order marks
73 then reads characters until the next newline or carriage return appears,
74 the nl or cr character itself is not appended to result) */
75/* (basically means two things: Empty lines will be skipped and windows' CR+NL
76 will not lead to reading extra empty lines.) */
77/* (result will be replaced with the read line if return value is 0, otherwise
78 result will not be altered in any way) */
79int readline_utf8(FILE *in, string *result);
80int readline_utf8(FILE *in, wstring *result);
82// Writing string and wstring to file (also writes CR+NL after the string)
83/* (if FILE is not in binary mode, some platforms(like windows) will do
84 a conversion from NL to CR+NL, so then actually CR+CR+NL will be written,
85 which is not really a problem for the readline functions above, this info
86 is just here, so you do not have to get confused about that, if you should
87 ever take a closer peek at the output file) */
88int writeline_utf8(FILE *out, string line);
89int writeline_utf8(FILE *out, wstring line);
91// Functions for strings that can store the full range of characters
92typedef basic_string<unsigned int> uistring;
93int readline_utf8(FILE *in, uistring *result);
94int writeline_utf8(FILE *out, uistring line);
96#endif // #if !defined(__DB_utf_eight_HEAD_INCLUDED)

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