FIX: Print Preview Problems for Chars with ASCII Values > 127

WINDOWS   | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
      - Microsoft Visual C++ 32-bit Edition, version 1.0
  

SYMPTOMS

Microsoft Foundation Classes (MFC) library applications may have problems performing a print preview of text that contains characters with ASCII values greater than 127. The problems can range from uneven spacing of the characters to a general protection fault (GPF) when you try to activate a Print Preview.

CAUSE

The routine "CPreviewDC::ComputeDeltas()", located in the file DCPREV.CPP, passes signed char values as the second and third parameters to the function "::GetCharWidth()". However, ::GetCharWidth() takes unsigned integer values for its second and third parameters. In the process of converting from a signed char to an unsigned int, the wrong value is passed to ::GetCharWidth(), and the function either returns incorrect values or causes a GPF.

RESOLUTION

To avoid the problem, you can modify the file DCPREV.CPP and declare the two variables "lpszCurChar" and "lpszStartRun" as being long pointers to unsigned const characters. See the "MORE INFORMATION" section, below, to see exactly what changes need to be made.

STATUS

Microsoft has confirmed this to be a bug in the products listed at the beginning of this article. This problem was corrected in MFC version 3.0, included with Visual C++ version 2.0.

MORE INFORMATION

The function CPreviewDC::ComputeDeltas(,) located in the source file DCPREV.CPP, declares and uses two variables called lpszCurChar and lpszStartRun. These two variables are declared as being of type LPCSTR (in other words, 32-bit pointers to a const signed char). To avoid the problem of the pointers referring the ::GetCharWidth() function to passing characters, declare the variables lpszCurChar and lpszStartRun as being 32-bit pointers to const unsigned chars. With versions 2.0 and 2.5 of the MFC library supplied with Visual C++ for Windows, versions 1.0 and 1.5, this can be done when you define a new type called "LPCTSTR" with the following typedef:

   typedef const unsigned char FAR * LPCTSTR;

The variables lpszCurChar and lpszStartRun should be declared as being of type LPCTSTR. To do this, make the changes listed below:

1. In the file DCPREV.CPP supplied with Visual C++ for Windows, versions 1.0 and 1.5, change lines 457 and 458 to read as follows:

         LPCTSTR lpszCurChar = (LPCTSTR)lpszString;
         LPCTSTR lpszStartRun = (LPCTSTR)lpszString;
   

2. Change lines 489 and 490 to read as follows:

         CSize sizeExtent = ::GetTextExtent(m_hAttribDC,(LPCSTR)lpszStartRun,
             nRunLength);
   
   

3. In the file DCPREV.CPP, supplied with Visual C++ for Windows NT, version 1.0, change lines 466 and 467 to read as follows:

         LPCTSTR lpszCurChar = lpszString;
         LPCTSTR lpszStartRun = lpszString;
   

4. After following steps 1 through 3, rebuild the MFC library. For more information on rebuilding the MFC library, refer to the Class Library User's Guide or to the README.TXT file located in the MFC\SRC directory.