Article ID: 111923
Article Last Modified on 11/21/2006
APPLIES TO
- Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.51
- Microsoft Visual C++ 1.52 Professional Edition
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Standard Edition
This article was previously published under Q111923
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");
Because x is a CString object, not a pointer, it is inappropriate to compare x to a null pointer.
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");
Additional query words: CString inequality 2.50 2.51 2.52 3.00 3.10 gpf NULL gp-fault
Keywords: kbhowto kbstring KB111923
