Behavior of global variable varies in different functions

I am writing a program which renames AVI file (add extension - needed for some reason) and then gets frame from it and stores it in BMP file.

Here are the important parts of code:

#include "stdafx.h"
#include "ImageProcessor2.h"
#include <windows.h>
#include <Commdlg.h>
#include <Commctrl.h>
#include <stdio.h>
#include <string>
#include "vfw.h"
#include <atlstr.h>

// Global Variables...
HINSTANCE g_hInst;
LPSTR selectedAVI=NULL;

INT_PTR CALLBACK DialogProc(HWND, UINT, WPARAM, LPARAM);
void OpenDialog(HWND);
void GetFrame(HWND);

int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPTSTR lpCmdLine, int nCmdShow)
{
    g_hInst = hInstance;
    DialogBox(hInstance, MAKEINTRESOURCE(IDD_MAIN), NULL,(DLGPROC)DialogProc);
    return 0;
}


INT_PTR CALLBACK DialogProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch ( uMsg )
    {
        case WM_INITDIALOG:
            SetClassLongPtr(hWnd, GCLP_HICONSM, 
                (LONG_PTR)LoadIcon(g_hInst, MAKEINTRESOURCE(IDI_IMAGEPROCESSOR2)));
            break;
        case WM_COMMAND:
            switch ( LOWORD(wParam) )
            {
                case IDCANCEL:
                    EndDialog(hWnd, LOWORD(wParam));
                    break;
                case IDB_LOADVID:
                    OpenDialog(hWnd);
                    break;
                case IDB_GETFRAME:
                    if (selectedAVI==0)
                        {
                            MessageBox(NULL, "Select the file by pressing Load button first", "Info", MB_OK);
                            break;
                        }
                    else
                    GetFrame(hWnd);
                    break;
            }
            break;
        break;
    }
    return FALSE;
}

void OpenDialog(HWND hWnd) 
{
  OPENFILENAME ofn;
  TCHAR szFile[MAX_PATH];
  char* renamedfile;

  ZeroMemory(&ofn, sizeof(ofn));
  ofn.lStructSize = sizeof(ofn);
  ofn.lpstrFile = szFile;
  ofn.lpstrFile[0] = '\0';
  ofn.hwndOwner = hWnd;
  ofn.nMaxFile = sizeof(szFile);
  ofn.lpstrFilter = TEXT("All files(*.*)\0*.*\0");
  ofn.nFilterIndex = 1;
  ofn.lpstrInitialDir = NULL;
  ofn.lpstrFileTitle = NULL;
  ofn.Flags = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;


    if (GetOpenFileName(&ofn))
        {
            //call to rename function
            ofn.lpstrFile=renamedfile;
            MCIWndCreate(GetDlgItem(hWnd, IDC_ANIRENDER), (HINSTANCE)g_hInst,WS_CHILD|WS_VISIBLE|WS_SYSMENU|MCIWNDF_NOOPEN|MCIWNDF_NOMENU|MCIWNDF_NOTIFYALL, ofn.lpstrFile);
            selectedAVI=ofn.lpstrFile;
            SetDlgItemTextA(hWnd, IDC_EDIT1, selectedAVI);
        }
}

//rename function is here

void GetFrame(HWND hWnd)
{
    LONG hr; 
    PAVIFILE pfi开发者_Go百科le;
    SetDlgItemTextA(hWnd, IDC_EDIT2, selectedAVI);

    AVIFileInit();          // opens AVIFile library 
    //further AVI processing functions are here
    AVIFileExit();          // releases AVIFile library 
}

Now please explain me why I am getting this:

in EDIT1: correct path to file (such as "D:\test\testAVI.avi")

in EDIT2: "îţîţîîţîţîîţîţî" and so on, ending with "ţ™Öj8p"

I think it should show the same strings because it reads from the same global variable. What am I doing wrong? How do it right?

Thank you

---

Because selectedAVI is a pointer and has no storage of its own, and the thing it's pointing to (which does have the storage) is part of a local variable (the OPENFILENAME structure in OpenDialog), which has gone out of scope and been overwritten by the time you get to IDC_EDIT2.

To fix this, change it to an array of length MAX_PATH and use strcpy or similar to assign to it. Then it should work the way you want.