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//////.rc
MAIN MENU DISCARDABLE
BEGIN
    POPUP "File "
 BEGIN
        MENUITEM "&Open",101              
    END
    MENUITEM "&Chart",  102
    MENUITEM "&About",  103
    MENUITEM "&Quit",    104
END
////

#include <windows.h>
#include <windowsx.h>
#include<stdlib.h>

#define MI_OPEN 101
#define MI_CHART 102
#define MI_ABOUT 103
#define MI_QUIT 104


float nCurrentScales=1;
short nBuf[500];
short nBufScaled[500];
BOOL bDataOK=FALSE;
char szFile[128];
char szFilter[]="Data Files(*.DAT)\0*.dat\0All Files(*.*)\0*.*\0";
OPENFILENAME ofn;
DWORD nCnt;

void OnDestroy(HWND hwnd)
{
//  MessageBox(hwnd,"The end","Exit",MB_OK);
    PostQuitMessage(0);
}



void OnCommand(HWND hwnd, int id, HWND, UINT)
{
    InvalidateRect(hwnd,NULL,TRUE);
    switch(id)
    {
    case MI_OPEN:
    //  MessageBox(hwnd,"Opening File ","Command",MB_OK);      
                         szFile[0] = 0;
        ZeroMemory(&ofn,sizeof(OPENFILENAME));
        ofn.lStructSize=sizeof(OPENFILENAME);
        ofn.hwndOwner=hwnd;
        ofn.lpstrCustomFilter=szFilter;
        ofn.lpstrFile=szFile;
        ofn.nMaxFile=sizeof(szFile);
        ofn.Flags=OFN_PATHMUSTEXIST|OFN_FILEMUSTEXIST;
        if(GetOpenFileName(&ofn))
        {
        HANDLE hFile=CreateFile(szFile,GENERIC_READ,0,0,OPEN_EXISTING,0,NULL);
        if(hFile==INVALID_HANDLE_VALUE)break;
        ReadFile(hFile,nBuf,2*500,&nCnt,NULL);
        CloseHandle(hFile);
        bDataOK=TRUE;
        for(int i=0;i<500;i++)
            nBufScaled=nBuf*nCurrentScales;
        InvalidateRect(hwnd,NULL,TRUE);
        break;
        }
//      else
            break;
        ////
    case MI_CHART:
        MessageBox(hwnd,"Chart","Command",MB_OK);
        break;
    case MI_about :
        MessageBox(hwnd," 1 ","About",MB_OK);
        break;
    case MI_QUIT:
        DestroyWindow(hwnd);
        break;
    }
}

LRESULT CALLBACK WndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
    switch(msg)
    {
    HANDLE_MSG(hwnd,WM_COMMAND,OnCommand);
        HANDLE_MSG(hwnd,WM_DESTROY,OnDestroy);
    default:
        return(DefWindowProc(hwnd,msg,wParam,lParam));
    }
}


int WINAPI WinMain(HINSTANCE hInst,HINSTANCE,LPSTR,int)
{
    char szClassName[]="MainWindow";
    char szTitle[]="1";
    MSG Msg;
    WNDCLASS wc;
    ZeroMemory(&wc, sizeof(wc));
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInst;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = GetStockBrush(LTGRAY_BRUSH);
    wc.lpszMenuName = "MAIN";
    wc.lpszClassName = szClassName;
    RegisterClass(&wc);
    HWND hwnd=CreateWindow(szClassName, szTitle,WS_OVERLAPPEDWINDOW,300,200,600,500,HWND_DESKTOP,NULL,hInst,NULL);
    ShowWindow(hwnd,SW_SHOWNORMAL);
    while(GetMessage(&Msg,NULL,0,0))
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return 0;
}

OPENFILENAME ofn;
TCHAR file_name[MAX_PATH];
TCHAR full_file_path[MAX_PATH];
ZeroMemory(&ofn, sizeof(ofn));
ofn.lStructSize = sizeof(ofn);
ofn.hwndOwner = NULL;
ofn.lpstrFile = full_file_path; // полный путь
ofn.lpstrFile[0] = '\0';
ofn.lpstrFileTitle = file_name;
ofn.lpstrFileTitle[0] = '\0';
ofn.nMaxFile = sizeof(full_file_path);
ofn.nMaxFileTitle = sizeof(file_name);
ofn.lpstrFilter = "Файлы(*.txt)\0*.txt\0";
ofn.nFilterIndex = 0;
ofn.lpstrInitialDir = NULL;
ofn.Flags = OFN_PATHMUSTEXIST | OFN_FILEMUSTEXIST;
       
if (GetOpenFileName(&ofn) == TRUE) {...}