HOWTO: Compare a CString to the Empty String

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

SUMMARY

The correct way to test a CString to see whether it is empty (or not empty) is to use the IsEmpty() member function as shown below:

   CString x = "This is a sample CString";
   if (x.IsEmpty())
      AfxMessageBox("The CString is EMPTY");
   else
      AfxMessageBox("The CString is not EMPTY");

MORE INFORMATION

The CString member function IsEmpty() tests a CString for the empty condition. The function returns nonzero if the string has zero length.

If the CString equality operators (==, !=) are used in an attempt to test whether a CString is NULL, a general protection (GP) fault may occur. The following code fragment demonstrates this:

   CString x = "This is a sample CString";
   if (x != NULL)  // GP Fault for (x == NULL) condition, as well
      AfxMessageBox("The CString is not EMPTY");
   else
      AfxMessageBox("The CString is EMPTY");

Testing a CString against the empty string, as shown below, is allowed. Because a temporary CString object is constructed, this method is less efficient than calling IsEmpty():

   CString x = "This is a sample CString";
   if (x != "")
      AfxMessageBox("The CString is not EMPTY");
   else
      AfxMessageBox("The CString is EMPTY");