Memory exception in program - file handling and strings

Question

I'm getting the following error: Unhandled exception at 0x7580b9bc in _ObjDraw.exe: Microsoft C++ exception: std::invalid_argument at memory location 0x0024f718..

When I run:

    ifstream file(fileName);
    if(!file)
    {
        return;
    }

    faces = vector<Face>();
    string number = "";
    Face tFace;

    while(!file.eof())
    {
        getline(file, Buffer);
        if(Buffer[0] == 'f')
        {
            //Faces have vertices, normals, and textures
            size_t firstSpace = Buffer.find_first_of(' ', 0);
            size_t firstSlash = Buffer.find_first_of('/', firstSpace + 1);
            size_t nextSpace  = Buffer.find_first_of(' ', firstSpace + 1);
            size_t nextSlash = Buffer.find_first_of('/', firstSlash + 1);

            if(firstSlash == string::npos) //Implies that there are no normals or textures
            {
                do
                {
                    //Get the vertex number and add it to the face
                    nextSpace = Buffer.find_first_of(' ', firstSpace + 1);
                    number.assign(Buffer, firstSpace + 1, nextSpace - 1);
                    tFace.addVertex(stoi(number));

                    //Move to the next vertex
                    firstSpace = nextSpace;
                }while(firstSpace != string::npos);
            }
            else //implies that there are textures and/or normals
            {
                if(nextSlash < nextSpace) //Normal's are present
                {
                    do
                    {
                        //Get the vertex number
                        number.assign(Buffer, firstSpace + 1, firstSlash - 1);
                        tFace.addVertex(stoi(number));

                        //Get the normal
                        number.assign(Buffer, firstSlash + 1, nextSlash - 1);
                        if(number != "")
                        {
                            tFace.addTexture(stoi(number));
                        }

                        //Get the texture
                        number.assign(Buffer, nextSlash + 1, nextSpace - 1);
                        if(number != "")
                        {
                            tFace.addNormal(stoi(number));
                        }

                        //Get next positions
                        firstSpace = nextSpace;
                        firstSlash = Buffer.find_first_of('/', firstSpace);
                        nextSlash = Buffer.find_first_of('/', firstSlash + 1);
                        nextSpace = Buffer.find_first_of(' ', firstSpace + 1);

                    }while(firstSpace != string::npos);
                }
                else //Only textures
                {
                    do
                    {
                        //Get the vertex number
                        number.assign(Buffer, firstSpace + 1, firstSlash - 1);
                        tFace.addTexture(stoi(number));

                        //Get the normal number
                        number.assign(Buffer, firstSlash + 1, nextSpace - 1);
                        tFace.addNormal(stoi(number));

                        firstSpace = nextSpace;
                        nextSpace = Buffer.find_first_of(' ', firstSpace + 1);
                        firstSlash = Buffer.find_first_of('/', firstSlash + 1);

                    }while(firstSpace != string::npos);
                }
            }
            //Add tFace to face vector
            faces.push_back(tFace);
            tFace = Face();
        }
    }
    file.close();
}

123.obj has the following contents: f 1//2 2//2 3//2 2//2 - This causes the exception Having f 1 2 3 4 or f 1/2/3 2/3/4 3/4/5 works as it should. It's only when there is a double slash that a problem occurs. When using the file with the '//', the first if statement should be false and the else block should be executed, but for some reason, it ends up entering the first loop. firstSlash is 3 and nextSlash is 4, when i output them to check. Face and Vertex are classes, with the appropriate member functions

Answer 1

Just turn on first chance exception catching (in the menus Debug ==> Exceptions... or CTRL+ALT E in VS 2010) and run it under debugger. It will stop immediately when the exception is thrown and you can go up the stack to your code and (maybe) understand what is wrong.

Answer 2

find_first_of doesn't throw, neither does a while or a comparison, so your error must be in one of the //code segments.

You should paste more code if you want an answer

--- after the edit---

The code could use a lot more checks, you only check for firstSpace != npos in your while condition, while nextSpace and firstSlash could easily be npos too during the next iteration.