MFC CString Format gives weird behaviour

2
votes

I am having a weird problem with CString I have the following code which gives an unexpected result:

CString sourcePath = _T("C:\\some\\path\\file.ext");
CString log;
log.Format(_T("Path = %s"), sourcePath);

the result string shows Path = (null).

I am not sure what is going on under the hood there, I have tried casting the sourcePath to an LPCTSTR and got a valid pointer and when viewing the content of that memory address in the memory view window of MSVC everything seems valid.

this annoys me as I have tried the same method in previous projects and it worked pretty well.

Thanks.

P.S. Please, before people start commenting here asking about what is a CString, as it happened in an earlier post of mine, please check here first: MSDN CString

Edit: sorry about the slash thingy.. and yes the original code does have double slashes..

4
c++visual-studiomfcc-strings
This sample doesn't reproduce the problem here. Have you checked for buffer overflows that could affect sourcePath? Is this your literal code, or does other things happen in between the 3 lines you've shown? - Erik
@Erik, I just tested this with Visual Studio 2010 and Visual Studio 2008 and was unable to duplicate the problem as well. There must be some other code going on in between. - Justin
Got the same problem. Oh, yes, I have some old projects with MFC ;) VS2012 and VS6 can reproduce this problem. My format string was "some text %s, some text: %d, %d, %s text %s". First string was ok, but the second and third are not - only "(null)". So I divided this massive format string into two smaller and now it looks good. Third string was added without format. One %s per format string. - crea7or

4 Answers

0
votes

As your MSDN CString link also mentions, you cannot pass the CString itself to the Format function.

Use:

  log.Format(_T("Path = %s"), sourcePath.GetString());
0
votes

The string "C:\some\path\file.ext" should be "C:\some\path\file.ext" - otherwise you will read control characters (\s \p \f) instead.

0
votes

Depending on the MFC version and whether your app is built for win32 or x64, you might have to cast the CString:

log.Format(_T("Path = %s"), (LPCTSTR)sourcePath);
0
votes

There is a problem in your sourcePath initialization. The character \ is a special character in C/C++. You should replace it with \ (double ) So the first line of code should be: CString sourcePath = _T("C:\\some\\path\\file.ext");

Hope this helps.