Question

Please have a glance at this program:

class CopyCon
{
public:
char *name;

CopyCon()
{ 
    name = new char[20];        
    name = "Hai";//_tcscpy(name,"Hai");
}

CopyCon(const CopyCon &objCopyCon)
{
    name = new char[_tcslen(objCopyCon.name)+1];
    _tcscpy(name,objCopyCon.name);
}

~CopyCon()
{
    if( name != NULL )
    {
        delete[] name;
        name = NULL;
    }
}
};

int main()
{
    CopyCon obj1;
    CopyCon obj2(obj1);
    cout<<obj1.name<<endl;
    cout<<obj2.name<<endl;
}

This program crashes on execution. Error: “Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)”

If I assign “Hai” to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign “Hai” to name, its working perfectly. Can some one explain why so?

Answer 1

In the default constructor

CopyCon()
{ 
    name = new char[20];        
    name = "Hai";//_tcscpy(name,"Hai");
}

you assign the address of a string literal to the pointer and in the destructor you call delete[] on it, that’s undefined behavior. delete[] should only be called on addresses returned by new[].

When you instead use _tcscpy() you copy the literal content to the buffer allocated by new[] and then the destructor runs fine.