Non-Const reference?

ChemicalBurn · 04-04-2005, 11:04 AM

Hi, I have a small problem with calling a function IsEdgeDisjoint, thing is I can call all member functions within the object except this one, I think because of the argument type. I dont know what the problem is, here's the code:

Code:

 bool IsEdgeDisjoint(const Path<NodeTPointer,EdgeTPointer>& otherPath);

This is the prototype for the function in the library,
and here's where Im calling it:

Code:

bool NetworkState::AreEdgeDisjoint(List<LSPEdge> path1, List<LSPEdge> path2){
  
  Path<LSPNode,LSPEdge> Path1;
  Path<LSPNode,LSPEdge> Path2;
  Path1.Edges(path1);
  Path2.Edges(path2);
  cout<<"Path1\n"<<Path1<<endl;
  return Path1.IsEdgeDisjoint(Path2);//This statement Generates the error    
}

But it generates this error:
/home/j_ghibril/GRAPH-v2.0/include/GRAPH/TPP/Path.tpp:284: error: invalid
initialization of non-const reference of type '
GRAPH::List<GRAPH::EdgeT<LSPNodeType, LSPEdgeType>*>&' from a temporary of
type 'GRAPH::List<GRAPH::EdgeT<LSPNodeType, LSPEdgeType>*>'
make: *** [NetworkState.o] Error 1

Anyone have any ideas?

Kdr Kane · 04-04-2005, 01:18 PM

Just a suggestion, but it sounds like the preprocessor needs to know about IsEdgeDisjoint before AreEdgeDisjoint.

Make sure your include statements or your declarations are in the correct order.

deiussum · 04-04-2005, 02:46 PM

It says the error is at:

/home/j_ghibril/GRAPH-v2.0/include/GRAPH/TPP/Path.tpp:284

Which sounds like it is seeing an error in the header that defines your Path template class... Post some code from your IsEdgeDisjoint method, and code around that line of the Path.tpp file.

When using templates, you should understand that unless a template function or class is actually used, it won't be compiled. So, the act of simply using a method that wasn't used before can uncover errors that previously appeared to compile. I'm guessing something like that could be happening here, but I can't say w/o more info.

ChemicalBurn · 04-05-2005, 03:54 AM

Im pretty sure the included file is fine, because it did compile it before when I used other functions in the class, but its this function specifically that is giving the error.
And sorry I forgot to mention, the error at line 284 is actuall the last line in the class (new line nothing in it) Thats why im confused. Though I was wondering about the meaning of the error "non-const reference" when does it usually come out?

@Kane, thanks for the tip, but I checked the header files, they were in proper order, but I switched the Path.h up to the top but still...

deiussum · 04-05-2005, 08:32 AM

Here's one example of a small program that can generate the non-const error you are seeing.

Code:

#include <iostream>
using namespace std;

class A
{
    public:
        A() {}
};


int main()
{
    A& a = NULL;

    return 0;
}

And here is a program that demonstrates what I was talking about with template classes and functions not getting compiled unless those specific functions are used

Code:

#include <iostream>
using namespace std;

template <typename T>
void Blah (T t)
{
    // Obvious compiler error here since a is not
    // declared anywhere.  Won't generate any errors
    // Unless the Blah function is called, though!!
    cout << t << a << endl;
}

int main()
{
    // Uncomment and the errors appear, leave commented
    // and no errors are reported because the Blah function
    // doesn't really get compiled

    //Blah(2);

    return 0;
}