STL Sample for the new operator Function

• The Standard C++ Library included with: - Microsoft Visual C++, 32-bit Edition, version 4.2

SUMMARY

The sample code below illustrates how to use the new operator from the Standard Library in Visual C++.

MORE INFORMATION

The new operator will return NULL or throw an exception on failure.

Required Header

   <new>

Prototype

   void *operator new(size_t n)
   void *operator new(size_t n, const nothrow&)
   void *operator new[](size_t n);

Description

The first operator new will attempt to allocate memory and if it fails, will throw an exception.

The second operator new accepts a second parameter of type nothrow. This parameter indicates that if the allocation fails, it should return NULL and not throw an exception.

The third operator new will allocate memory for an array of that type and if it fails, will throw an exception.

Sample Code

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// <filename> :  newop.cpp
//
// Functions:
//
//    void *operator new(size_t n)
//
//    void *operator new(size_t n, const nothrow&)
//
//    void *operator new[](size_t n);
//
// Written by Linda Koontz
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
//////////////////////////////////////////////////////////////////////

/* Compile options needed: /GX
*/

#include <new>
#include <iostream>

    BigClass() {};
    ~BigClass(){}
        double BigArray[99999999];
};

void main()

    try {
    BigClass * p = new BigClass;
    }
    catch( bad_alloc a) {
        const char * temp = a.what();
        cout << temp << endl;
        cout << "Threw a bad_alloc exception" << endl;
    }
    BigClass * q = new(nothrow) BigClass;
    if ( q == NULL )
        cout << "Returned a NULL pointer" << endl;

    try {
    BigClass * r = new BigClass[3];
    }
    catch( bad_alloc a) {
        const char * temp = a.what();
        cout << temp << endl;
        cout << "Threw a bad_alloc exception" << endl;
    }

Program Output is:

bad allocation Threw a bad_alloc exception Returned a NULL pointer bad allocation Threw a bad_alloc exception

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference. Query on “operator new,” or look in Help for the <new> header file.

NOTE: The Online Help for the new header file lists the following prototypes for the new operators demonstrated in this article:

    void *operator new(size_t n) throw(bad_alloc);

    void *operator new(size_t n, const nothrow&) throw();

    void *operator new[](size_t n) throw(bad_alloc);

   Microsoft C++ does not support the function exception
   specification mechanism, as described in section 15.4 of the
   ANSI C++ draft.

   void Func() throw (ProblemOne, ProblemTwo) {}

    void Func() {
    {
    try {}
    catch (ProblemOne) {}
    catch (ProblemTwo) {}
    catch (...) { unexpected(); }
    }