BUG: The CString::Delete() Function Does Not Return the Correct Value (250321)

The information in this article applies to:

The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++, 32-bit Enterprise Edition 6.0
- Microsoft Visual C++, 32-bit Professional Edition 6.0
- Microsoft Visual C++, 32-bit Learning Edition 6.0

This article was previously published under Q250321

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 that this is a bug in the Microsoft products that are listed at the beginning of this article.

MORE INFORMATION

Steps to Reproduce Behavior

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

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);

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

You should see in the output window that the return value from the Delete method is the length of the original string, not the length of modified string.

Modification Type:	Major	Last Reviewed:	12/11/2003
Keywords:	kbBug kbpending kbString KB250321