c++ Operator overloading "-"

Question

I've done operator overloading to "-" for my class graph. It's use isn't totally intuitive (bad coding-I know) but if I do graph3 = graph2-graph1 then graph 3 is supposed to receive only those vertexes in both graph 2 and graph 1.

So, I've written the code and when I run the debugger, the operator- function seems to create a new "graph" to return and it adds the appropriate vertexes to the new graph and then the debugger seems to exit the op- function, but never makes it back to main. It's as if it's waiting for me to enter something. No error messages appear.

Here is the code:

char stringy[100];
//cin>>stringy;
strcpy(stringy,"|12,34,25,2,3,2|(3->2),(2->1),(5->9),(2->1)|");
char* param= new char[sizeof(stringy)];
strcpy(param,stringy);
Graph graph1(param);

 char sstring[20] = "|33,34,11|(2->33)|";
Graph graph2(sstring);
cout<<graph2.outSumm()<<endl;

Graph graph3;
//until here everything works fine
graph3= graph1-graph2; //the debugger does this and then 

cout<<graph3.outSumm()<<endl;

The operator- function:

Graph Graph::operator- (const Graph& g2) const
{
Graph created;

//goes through "this" list and if value exists in g2 copies it to created
for(int i=0;i<vertList.getSize();i++)
{
 if (g2.vertList.find(vertList.read(i))!=999)
 created.addVertex(vertList.read(i).getInt());
}

return created;
}

I'm using codeblocks.

Copy constructor:

Graph(const Graph& g2):      
maxVal(g2.maxVal),vertList(g2.vertList),edgeList(g2.edgeList){} ;

Assignment operator:

void Graph::operator= (const Graph& g2)
{
 if (this==&g2)
 {
 cout<<"not the greatest idea"<<endl;
 return;
 }

 vertList.delete_List();
 edgeList.delete_List();
 maxVal=0;

addValues(g2.outSumm());
}

Answer 1

Not specifically related to your question (though it might be), why are you not using std::string? And if you must use character arrays, why not:

char stringy[100] = "|12,34,25,2,3,2|(3->2),(2->1),(5->9),(2->1)|";
Graph graph1( stringy );

or even:

Graph graph1( "|12,34,25,2,3,2|(3->2),(2->1),(5->9),(2->1)|" );

Or are you storing the pointer passed into the constructor in your class? If so, that is a bad idea, and my advice to use std::strings goes double.

Answer 2

Sounds like your code is in an infinite loop. Have you tried breaking in the debugger when the program appears to halt?

Do you have a copy constructor defined in the Graph class? You need that in order to successfully return a value using the local created variable.

Answer 3

Instead of implementing operator-, implement operator-= instead:

Graph& Graph::operator-=(const Graph& rhs)
{
    // remove nodes not in both Graphs

    return *this;
}

Then just implement operator- in terms of that:

Graph Graph::operator-(const Graph& rhs)
{
    Graph temp(*this);
    temp -= rhs;
    return temp;
}

See if this works.