DOCUMENT:Q158199  27-MAR-2002  [visualc]
TITLE   :STL Sample for the string::operator== Function
PRODUCT :Microsoft C Compiler
PROD/VER::4.2,5.0,6.0
OPER/SYS:
KEYWORDS:kbcode kbVC420 kbVC500 kbVC600 kbDSupport

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - The Standard C++ Library, used with:
    - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
    - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
    - Microsoft Visual C++.NET (2002) 
-------------------------------------------------------------------------------

SUMMARY
=======

The sample code below illustrates how to use the string::operator== STL function
in Visual C++.

MORE INFORMATION
================

Required Header
---------------

      <string>

Prototype
---------

      Function 1:
      template<class _E, class _TYPE, class _A> inline
          bool operator==(const basic_string<_E, _TYPE, _A>& LString,
              const _E *RCharArray);

      Function 2:
      template<class _E, class _TYPE, class _A> inline
          bool operator==(const _E * LCharArray,
              const basic_string<_E, _TYPE, _A>& RString);

      Function 3:
      template<class _E, class _TYPE, class _A> inline
          bool operator==(const basic_string<_E, _TYPE, _A>& LString,
              const basic_string<_E, _TYPE, _A>& RString);

NOTE: The class/parameter names in the prototype may not match the version in the
header file. Some have been modified to improve readability.

Description
-----------

There are three versions of the string::operator== function. The first two
functions compare a null-terminated character array against a basic_string. They
perform this operation by using the basic_string's string::compare function and
returning true if the compare function returns a 0 value. The third function
compares two basic_string variables, using the string::compare function of the
first basic_string variable. For more information on the compare function,
please see the string::compare function.

Note that this operator does not work with NULL pointer for the character array.
You will need to make sure that the character array is not NULL before you pass
it to the operator.

Sample Code
-----------

   ////////////////////////////////////////////////////////////////////// 
   // 
   // Compile options needed: /GX
   // 
   // StringEqual.cpp: Illustrates how to use the operator== to test for
   //                  equality of a basic_string variable and a
   //                  null-terminated string. It also illustrates how to
   //                  use the operator== to test for equality of two
   //                  basic_string variables.
   // 
   // Functions:
   // 
   //    operator==   returns true if the basic_string and the null-
   //                 terminated string are equal.
   //    operator==   returns true if both basic_strings are equal.
   // 
   // Written by Derek Jamison
   // of Microsoft Product Support Services,
   // Copyright (c) 1996 Microsoft Corporation. All rights reserved.
   ////////////////////////////////////////////////////////////////////// 

   #pragma warning(disable:4786)

   #include <string>
   #include <iostream>
   using namespace std;

   #if _MSC_VER > 1020   // if VC++ version is > 4.2
      using namespace std;  // std c++ libs implemented in std
      #endif

   void trueFalse(int x)

   {
     cout << (x? "True": "False") << endl;
   }

   void main()

   {

      string S1="ABC";
      string S2="ABC";
      string S3="DEF";
      string S4; //This specifies an empty initial-controlled sequence.
      char CP1[]="abc";
      char CP2[]="DEF";
      char *CP3 = NULL;

      cout << "S1 is " << S1 << endl;
      cout << "S2 is " << S2 << endl;
      cout << "S3 is " << S3 << endl;
      cout << "S4 is " << S4 << endl;
      cout << "CP1 is " << CP1 << endl;
      cout << "CP2 is " << CP2 << endl;

      cout << "S1==CP1 returned ";
      trueFalse(S1==CP1);  // False    (calls function 1)

      cout << "S1==CP2 returned ";
      trueFalse(S1==CP2);  // False   (calls function 1)

      cout << "CP1==S1 returned ";
      trueFalse(CP1==S1);  // False    (calls function 2)

      cout << "CP2==S1 returned ";
      trueFalse(CP2==S1);  // False   (calls function 2)

      cout << "S1==S2 returned ";
      trueFalse(S1==S2);   // True    (calls function 3)

      cout << "S1==S3 returned ";
      trueFalse(S1==S3);   // False   (calls function 3)

      cout << "S1==S4 returned ";
      trueFalse(S1==S4);   // False   (calls function 3)

      // Following use of the operator will cause the program to
      // crash since CP3 is NULL.
      // cout << "S1==CP3 returned ";
      // trueFalse(S1==CP3);

   }

Program Output
--------------

   S1 is ABC
   S2 is ABC
   S3 is DEF
   S4 is
   CP1 is abc
   CP2 is DEF
   S1==CP1 returned False
   S1==CP2 returned False
   CP1==S1 returned False
   CP2==S1 returned False
   S1==S2 returned True
   S1==S3 returned False
   S1==S4 returned False

REFERENCES
==========

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample operator== string

======================================================================
Keywords          : kbcode kbVC420 kbVC500 kbVC600 kbDSupport 
Technology        : kbVCsearch kbAudDeveloper kbVCLibrary
Version           : :4.2,5.0,6.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2002.