Article ID: 158206 - Last Review: January 11, 2006 - Revision: 4.0

How to use the string::operator!= STL function in Visual C++

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This article was previously published under Q158206
Note Microsoft Visual C++ .NET 2002 and Microsoft Visual C++ .NET 2003 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code. Microsoft Visual C++ 2005 supports both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model.

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SUMMARY

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

Required Header

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

There are two versions of the string::operator!= function. Both versions are used to compare a null-terminated character array against a basic_string. They perform this operation by negating the result of (LString==RCharArray) or (LCharArray==RString). For more information on this comparison, please see the string::operator== function.

Notice 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.
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Sample Code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: /GX
// 
// StringNotEqual.cpp : Illustrates how to use the operator!= to test for
//                      non-equality of a basic_string variable and a
//                      null-terminated string.
// 
// Functions:
// 
//    operator!=   Returns true if the basic_string and the null-
//                 terminated string are not 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>

#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";
   char CP1[]="ABC";
   char CP2[]="DEF";
   char CP3[]="abc";

   cout << "S1 is " << S1 << endl;
   cout << "CP1 is " << CP1 << endl;
   cout << "CP2 is " << CP2 << endl;
   cout << "CP3 is " << CP3 << endl;

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

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

   cout << "S1!=CP3 returned ";
   trueFalse(S1!=CP3);  // True   (calls function 1)

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

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

   cout << "CP3!=S1 returned ";
   trueFalse(CP3!=S1);  // True   (calls function 2)

}
Program Output is: 
S1 is ABC
CP1 is ABC
CP2 is DEF
CP3 is abc
S1!=CP1 returned False
S1!=CP2 returned True
S1!=CP3 returned True
CP1!=S1 returned False
CP2!=S1 returned True
CP3!=S1 returned True
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REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.
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APPLIES TO
  • The Standard C++ Library, when used with:
    • Microsoft Visual C++ 4.2 Enterprise Edition
    • Microsoft Visual C++ 5.0 Enterprise Edition
    • Microsoft Visual C++ 6.0 Enterprise Edition
    • Microsoft Visual C++ 4.2 Professional Edition
    • Microsoft Visual C++ 5.0 Professional Edition
    • Microsoft Visual C++ 6.0 Professional Edition
    • Microsoft Visual C++ 6.0 Standard Edition
    • Microsoft Visual C++ 2005 Express Edition
    • Microsoft Visual C++ .NET 2003 Standard Edition
    • Microsoft Visual C++ .NET 2002 Standard Edition
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Keywords: 
kbhowto kbinfo kbtemplate kbstl kbcode KB158206
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