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Posted 12 May 2003


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CStdioFile-derived class for multibyte and Unicode reading and writing

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19 Jul 2007CPOL3 min read
A class, derived from CStdioFile, which transparently reads and writes both Unicode and multibyte files. Version 1.5.

Demo app screenshot


This is a class derived from CStdioFile which transparently handles the reading and writing of Unicode text files as well as ordinary multibyte text files.

The code compiles as both multibyte and Unicode. In Unicode, multibyte files will be read and their content converted to Unicode using the current code page. In multibyte compilations, Unicode files will be read and converted to multibyte text.

The identification of a Unicode text file depends entirely on the presence of the Unicode byte order mark (0xFEFF). Its absence is not an absolute guarantee that a file is not Unicode, but it's the only method I use here. Feel free to suggest improvements.

By default, the class writes multibyte files, but can optionally write Unicode.


The ability to transparently handle both multibyte and Unicode seems to be such a fundamental requirement, that I was sure that there would already be something similar on offer, and yet nothing turned up. Did I miss something?

I needed it for a translation tool I wrote, and knocked together an implementation that was good enough for my needs. This is little more than a cleaned up version of that, so expect bugs and all manner of deficiencies. I've tested the demo app though with the basic combinations -- Unicode files in a multibyte compilation, Unicode-Unicode, Multibyte-Unicode, and Multibyte-Multibyte, and they all seem to work.

Using the code

The use of the class is pretty simple. It overrides three functions of CStdioFile: Open(), ReadString() and WriteString(). To write a Unicode file, add the flag CStdioFileEx::modeWriteUnicode to the flags when calling the Open() function.

In other respects, usage is identical to CStdioFile.

To find out if a file you have opened is Unicode, you can call IsFileUnicodeText().

To get the number of characters in the file, you can call GetCharCount(). This is unreliable for multibyte/UTF-8, however.

An example of writing in Unicode:

// Test writing
CStdioFileEx fileWriteUnicode;

if (fileWriteUnicode.Open(_T("c:\\testwrite_unicode.txt"), 
    CFile::modeCreate | CFile::modeWrite | CStdioFileEx::modeWriteUnicode))
    fileWriteUnicode.WriteString(_T("Unicode test file\n"));
    fileWriteUnicode.WriteString(_T("Writing data\n"));

You can now also specify the code page for multibyte file reading or writing. Simply call SetCodePage() before a read to tell CStdioFileEx which code page the file is coded in, or before a write, to tell it which code page you want it written in. Specifying CP_UTF8 as the code page allows you to read or write UTF-8 files.

The demo app is a dialog which opens a file, tells you whether it's Unicode or not and how many characters it contains, and shows the first fifteen lines from it. In the last couple of iterations I've added the option to convert a Unicode file to multibyte, and a multibyte file to Unicode, and a combo to specify the code page when reading.

As of v1.6, there is no limitation on the length of the line that can be read in any mode (Multibyte/Unicode, Unicode/Multibyte, etc.).

I'd love to hear of people's experiences with it, as well as reports of bugs, problems, improvements, etc.

Oh, and if I've accidentally included something offensive in the demo dialog, let me know. My Arabic and Chinese are not all that good.


  • v1.0 - Posted 14 May 2003
  • v1.1 - 23 August 2003. Incorporated fixes from Dennis Jeryd
  • v1.2 - 06 January 2005. Fixed garbage at end of file bug (Howard J Oh)
  • v1.3 - 19 February 2005. Howard J Oh's fix mysteriously failed to make it into the last release. Improved the test program. Fixed miscellaneous bugs
    Very important: In this release, ANSI files written in ANSI are no longer written using WriteString. This means \n will no longer be "interpreted" as \r\n. What you write is what you get
  • v1.4 - 26 February 2005. Fixed submission screw-up
  • v1.5 - 18 November 2005. Code page can be specified for reading and writing (inc. UTF-8). Multibyte buffers properly calculated. Fix from Andy Goodwin
  • v1.6 - 19 July 2007. Major rewrite: Maximum line length restriction removed; Use of strlen/lstrlen eliminated. Conversion functions always used to calculate required buffers; \r or \n characters no longer lost; BOM writing now optional; UTF-8 reading and writing works properly; systematic tests are now included with the demo project


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

David Pritchard
Software Developer (Senior)
Spain Spain
I'm originally from Leek, Staffordshire in the UK, but I now work as a C++/MFC developer in Madrid, Spain.

I followed an erratic study/career path from German to a PhD in something resembling political science and linguistics, eventually ending up in IT.

I'm still finding bustling streets, warm nights, beer and vitamin D a pretty heady combination.

Comments and Discussions

GeneralRe: only ascii string Pin
David Pritchard18-Jul-07 15:14
MemberDavid Pritchard18-Jul-07 15:14 
QuestionWhy WriteString don't implement carriage return–linefeed pair Pin
fuochi11-May-06 2:29
Memberfuochi11-May-06 2:29 
AnswerRe: Why WriteString don't implement carriage return–linefeed pair Pin
David Pritchard18-Jul-07 15:06
MemberDavid Pritchard18-Jul-07 15:06 
GeneralDetecting Unicode Files Without BOM Pin
JeffWebFeat27-Apr-06 7:46
MemberJeffWebFeat27-Apr-06 7:46 
GeneralRe: Detecting Unicode Files Without BOM Pin
JeffWebFeat27-Apr-06 12:09
MemberJeffWebFeat27-Apr-06 12:09 
GeneralRe: Detecting Unicode Files Without BOM Pin
JeffWebFeat28-Apr-06 5:43
MemberJeffWebFeat28-Apr-06 5:43 
GeneralRe: Detecting Unicode Files Without BOM Pin
David Pritchard29-Apr-06 10:11
MemberDavid Pritchard29-Apr-06 10:11 
GeneralRe: Detecting Unicode Files Without BOM Pin
Kuji12-Jul-06 3:59
MemberKuji12-Jul-06 3:59 
GeneralBug in ParseFlags Pin
Konrad Windszus1-Apr-06 23:26
MemberKonrad Windszus1-Apr-06 23:26 
GeneralRe: Bug in ParseFlags Pin
David Pritchard2-Apr-06 11:52
MemberDavid Pritchard2-Apr-06 11:52 
GeneralRe: Bug in ParseFlags Pin
Konrad Windszus5-Apr-06 8:15
MemberKonrad Windszus5-Apr-06 8:15 
GeneralRe: Bug in ParseFlags Pin
David Pritchard5-Apr-06 10:24
MemberDavid Pritchard5-Apr-06 10:24 
GeneralBug in V 1.5 Pin
Konrad Windszus29-Mar-06 9:09
MemberKonrad Windszus29-Mar-06 9:09 
GeneralRe: Bug in V 1.5 Pin
David Pritchard29-Mar-06 10:02
MemberDavid Pritchard29-Mar-06 10:02 
GeneralA very nice class Pin
copernican3-Feb-06 22:33
Membercopernican3-Feb-06 22:33 
GeneralRe: A very nice class Pin
David Pritchard5-Feb-06 3:09
MemberDavid Pritchard5-Feb-06 3:09 
QuestionHelp, Release compiling error? Pin
peter_ywf29-Nov-05 2:07
Memberpeter_ywf29-Nov-05 2:07 
AnswerRe: Help, Release compiling error? Pin
David Pritchard29-Nov-05 8:56
MemberDavid Pritchard29-Nov-05 8:56 
GeneralRe: Help, Release compiling error? Pin
peter_ywf1-Dec-05 4:25
Memberpeter_ywf1-Dec-05 4:25 
GeneralRe: Help, Release compiling error? Pin
David Pritchard1-Dec-05 9:57
MemberDavid Pritchard1-Dec-05 9:57 
GeneralNon-English ANSII characters are not REALLY converted into Unicode by Windows XP Pin
chesscafe200328-Oct-05 21:55
Memberchesscafe200328-Oct-05 21:55 
GeneralRe: Non-English ANSII characters are not REALLY converted into Unicode by Windows XP Pin
David Pritchard17-Nov-05 13:14
MemberDavid Pritchard17-Nov-05 13:14 
GeneralRe: Non-English ANSII characters are not REALLY converted into Unicode by Windows XP Pin
chesscafe200325-Nov-05 5:33
Memberchesscafe200325-Nov-05 5:33 
GeneralRe: Non-English ANSII characters are not REALLY converted into Unicode by Windows XP Pin
David Pritchard25-Nov-05 8:10
MemberDavid Pritchard25-Nov-05 8:10 
GeneralRe: Non-English ANSII characters are not REALLY converted into Unicode by Windows XP Pin
chesscafe20032-Dec-05 12:53
Memberchesscafe20032-Dec-05 12:53 

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