BUG: The CString::Delete() Function Does Not Return the Correct Value

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

The CString::Delete function returns the length of the original string instead of the length of the modified string.

CAUSE

The CString::Delete function initializes a local variable (nNewLength) with the length of the original string and does not change this variable to reflect the length of the changed string.

Here is the source code for the Delete method of the CString class (reproduced from the Strex.cpp file, which is located in the Mfc/Src folder):

int CString::Delete(int nIndex, int nCount /* = 1 */)
{
	if (nIndex < 0)
		nIndex = 0;
	int nNewLength = GetData()->nDataLength;
	if (nCount > 0 && nIndex < nNewLength)
	{
		CopyBeforeWrite();
		int nBytesToCopy = nNewLength - (nIndex + nCount) + 1;

		memcpy(m_pchData + nIndex,
			m_pchData + nIndex + nCount, nBytesToCopy * sizeof(TCHAR));
		GetData()->nDataLength = nNewLength - nCount;
	}

	return nNewLength;
} 

RESOLUTION

To work around this problem, call the GetLength method on the modified CString class to get its length:

CString str2 = "Hockey is best!";
str2.Delete(6, 3);
int n = str2.GetLength(); 

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a dialog box-based application by using MFC AppWizard.



2. Place a button on the dialog box and create a handler for it. Copy the following code to the button's handler:
   

   
      //The following example demonstrates the use of CString::Delete:
      CString str2 = "Hockey is best!";
      TRACE("Length of the original string: %d\n", str2.GetLength());
      int n = str2.Delete(6, 3);
      TRACE("Actual length of the modified string: %d\n", str2.GetLength());
      TRACE("Return value from Delete method: %d\n",n);    




3. Compile and run the application under the Visual C++ debugger by pressing F5. Click the button.

© Microsoft Corporation 2000, All Rights Reserved.
Contributions by Sreedhar Pelluru, Microsoft Corporation

Additional query words: CString delete length return

Keywords : kbMFC kbString kbVC600bug kbDSupport kbGrpMFCATL
Version : winnt:6.0
Platform : winnt
Issue type : kbbug