既然您知道了如何建立清单方块，如何使用文字项目填入清单方块，如何接收来自清单方块的控件以及如何取得字符串，现在是到了写一个应用程序的时候了。如程序9-5中所示，ENVIRON程序在显示区域中使用清单方块来显示目前操作系统环境变量（例如PATH和WINDIR）。当您选择一个环境变量时，其内容将显示在显示区域的顶部。
程序9-5 ENVIRON
ENVIRON.C /*------------------------------------------------------------------------- ENVIRON.C -- Environment List Box (c) Charles Petzold, 1998 ---------------------------------------------------------------------------*/ #include <windows.h> #define ID_LIST 1 #define ID_TEXT 2 LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ; int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow) { static TCHAR szAppName[] = TEXT ("Environ") ; HWND hwnd ; MSG msg ; WNDCLASS wndclass ; wndclass.style = CS_HREDRAW | CS_VREDRAW ; wndclass.lpfnWndProc = WndProc ; wndclass.cbClsExtra = 0 ; wndclass.cbWndExtra = 0 ; wndclass.hInstance = hInstance ; wndclass.hIcon = LoadIcon (NULL, IDI_APPLICATION) ; wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ; wndclass.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1) ; wndclass.lpszMenuName = NULL ; wndclass.lpszClassName = szAppName ; if (!RegisterClass (&wndclass)) { MessageBox ( NULL, TEXT ("This program requires Windows NT!"), szAppName, MB_ICONERROR) ; return 0 ; } hwnd = CreateWindow (szAppName, TEXT ("Environment List Box"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL) ; ShowWindow (hwnd, iCmdShow) ; UpdateWindow (hwnd) ; while (GetMessage (&msg, NULL, 0, 0)) { TranslateMessage (&msg) ; DispatchMessage (&msg) ; } return msg.wParam ; } void FillListBox (HWND hwndList) { int iLength ; TCHAR * pVarBlock, * pVarBeg, * pVarEnd, * pVarName ; pVarBlock = GetEnvironmentStrings () ; // Get pointer to environment block while (*pVarBlock) { if (*pVarBlock != '=') // Skip variable names beginning with '=' { pVarBeg = pVarBlock ; // Beginning of variable name while (*pVarBlock++ != '=') ; // Scan until '=' pVarEnd = pVarBlock - 1 ; // Points to '=' sign iLength = pVarEnd - pVarBeg ; // Length of variable name // Allocate memory for the variable name and terminating // zero. Copy the variable name and append a zero. pVarName = calloc (iLength + 1, sizeof (TCHAR)) ; CopyMemory (pVarName, pVarBeg, iLength * sizeof (TCHAR)) ; pVarName[iLength] = '\0' ; // Put the variable name in the list box and free memory. SendMessage (hwndList, LB_ADDSTRING, 0, (LPARAM) pVarName) ; free (pVarName) ; } while (*pVarBlock++ != '\0') ; // Scan until terminating zero } FreeEnvironmentStrings (pVarBlock) ; } LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam,LPARAM lParam) { static HWND hwndList, hwndText ; int iIndex, iLength, cxChar, cyChar ; TCHAR * pVarName, * pVarValue ; switch (message) { case WM_CREATE : cxChar = LOWORD (GetDialogBaseUnits ()) ; cyChar = HIWORD (GetDialogBaseUnits ()) ; // Create listbox and static text windows. hwndList = CreateWindow (TEXT ("listbox"), NULL, WS_CHILD | WS_VISIBLE | LBS_STANDARD, cxChar, cyChar * 3, cxChar * 16 + GetSystemMetrics (SM_CXVSCROLL), cyChar * 5, hwnd, (HMENU) ID_LIST, (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE), NULL) ; hwndText = CreateWindow (TEXT ("static"), NULL, WS_CHILD | WS_VISIBLE | SS_LEFT, cxChar, cyChar, GetSystemMetrics (SM_CXSCREEN), cyChar, hwnd, (HMENU) ID_TEXT, (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE), NULL) ; FillListBox (hwndList) ; return 0 ; case WM_SETFOCUS : SetFocus (hwndList) ; return 0 ; case WM_COMMAND : if (LOWORD (wParam) == ID_LIST && HIWORD (wParam) == LBN_SELCHANGE) { // Get current selection. iIndex = SendMessage (hwndList, LB_GETCURSEL, 0, 0) ; iLength = SendMessage (hwndList, LB_GETTEXTLEN, iIndex, 0) + 1 ; pVarName = calloc (iLength, sizeof (TCHAR)) ; SendMessage (hwndList, LB_GETTEXT, iIndex, (LPARAM) pVarName) ; // Get environment string. iLength = GetEnvironmentVariable (pVarName, NULL, 0) ; pVarValue = calloc (iLength, sizeof (TCHAR)) ; GetEnvironmentVariable (pVarName, pVarValue, iLength) ; // Show it in window. SetWindowText (hwndText, pVarValue) ; free (pVarName) ; free (pVarValue) ; } return 0 ; case WM_DESTROY : PostQuitMessage (0) ; return 0 ; } return DefWindowProc (hwnd, message, wParam, lParam) ; }