Question

i’m fairly new to programming and still have no idea why its happening or how to fix this exception im getting when running this program i’m making…
How do exceptions occur anyway? Well here’s the code:

#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
using namespace std;

/////////////////////////   SCREEN CLASS    ////////////////////////////
class Screen
{
private:
///////////////////////////////////////////  Screen Variables //////////////
    string _name;
    string _contents[56];

public:
    Screen(){};
    ~Screen(){};
//////////////////////////////////////////// Display    ///////////////
    void Display()
    {

        for (int I = 0; I <56; I++)
        {
            cout << _contents[I];
        }
    };
///////////////////////////////////////////  Insert ///////////////////////
    bool Insert(vector <string> _string)
    {
        vector<string>::const_iterator I;
        int y = 0;
        for (I = _string.begin(); I != _string.end(); I++)
        {
            _contents[y] = _string[y];
            y++;
        }
        return true;
    };


};

/////////////////////////////////////////////  Main ////////////////////////
int main()
{
    vector <string> Map(56); 
    string _lines_[] = {"Hi", "Holla", "Eyo", "Whatsup", "Hello"};

    int offset = 0;
    for (vector <string>::const_iterator I = Map.begin(); I != Map.end(); I++)
    {
        Map[offset] = _lines_[offset];
        offset++;
    }

    Screen theScreen;
    theScreen.Insert(Map);
    theScreen.Display();

    char response;
    cin >> response;
    return 0;

}

I’m getting this exception:

First-chance exception at 0x5acfc9c7 (msvcr100d.dll) in TestGame.exe: 0xC0000005: Access violation reading location 0xcccccccc.
Unhandled exception at 0x5acfc9c7 (msvcr100d.dll) in TestGame.exe: 0xC0000005: Access violation reading location 0xcccccccc.

pointing to this line of code in “memcpy.asm”:

185        rep     movsd           ;N - move all of our dwords

Thanks!!

Answer 1

You create a vector with 56 elements in it:

vector <string> Map(56); 

Then you define an array containing five string objects in it:

string _lines_[] = {"Hi", "Holla", "Eyo", "Whatsup", "Hello"};

Then you try to read 56 string objects from that array:

                                     v 56 elements between begin() and end()
for (vector <string>::const_iterator I = Map.begin(); I != Map.end(); I++)
{
    Map[offset] = _lines_[offset];
                  ^ reading from the I'th element of the array

Since there are only five elements in the array, you are reading uninitialized memory (or memory that is initialized but probably doesn’t contain string objects) and treating that memory as if it contains string objects.

I’m not quite sure what you’re trying to do, but why not just insert the strings directly into the vector?

vector<string> Map;
Map.push_back("Hi");
Map.push_back("Holla");
// etc.

Or use the std::copy algorithm:

int elements_in_lines = sizeof(_lines_) / sizeof(_lines_[0]);
std::copy(_lines_, _lines_ + elements_in_lines, std::back_inserter(Map));