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Simple Class Question

Posted on 2009-04-08
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Last Modified: 2012-05-06
Hello,

I am an experienced VB.NET programmer, trying to get a handle on C++ (console only, not Visual C++).  I am having a problem with using classes.

In VB.NET you can globally declare an instance of a class that's not initialized.   Then, later on, when an event occurs you can initialize it.  (e.g. MyString = New String)  It will then execute the code in the constructor.

How can I accomplish this in C++?

Thanks,
-Torrwin


int _tmain(int argc, _TCHAR* argv[])
{
	//Declare a global instance of the File class
         File myFile;
 
	cout << "Please select one of the following options:\n";
	cout << "1) Setup a File\n";
	
	cin >> iChoice;
 
	if (iChoice == 1) 
	{
                  //This next line doesn't work in C++, what should it be?
	         myFile = New File;
	}
	else
	{
		cout << "Invalid choice.\n";
	}
 
	return 0;
}

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Question by:Torrwin
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3 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 2000 total points
ID: 24098856
In your cade, you would use the 'new' operator along with a pointer, e.g.
int _tmain(int argc, _TCHAR* argv[])
{
        //Declare an instance of a File class pointer
         File* myFile;
 
        cout << "Please select one of the following options:\n";
        cout << "1) Setup a File\n";
        
        cin >> iChoice;
 
        if (iChoice == 1) 
        {
                  
                 myFile = new File;
        }
        else
        {
                cout << "Invalid choice.\n";
        }
 
        delete myFile; // required to not create memory leaks
 
        return 0;
}

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LVL 86

Expert Comment

by:jkr
ID: 24098892
BTW, see also http://www.cplusplus.com/doc/tutorial/dynamic/ for more on that issue.
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 24099749
Make sure to initialize the pointer to 0 when declaring it. Or, in jkr's code, the delete at the end of main might cause unexpected results.
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