Article: Q111923
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,4.0,5.0
Operating System(s):
Keyword(s): kbMFC kbString kbVC kbGrpDSMFCATL
Last Modified: 07-MAY-2001
-------------------------------------------------------------------------------
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used with:
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
- Microsoft Visual C++, 32-bit Editions, 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");
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 : kbMFC kbString kbVC kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC
Version : winnt:1.0,2.0,2.1,4.0,5.0
Issue type : kbhowto
=============================================================================