为什么没有将编辑框中内容保存到文件中？（昨天得人指点后还是没有试出来）急

以下是代码：经过调试发现执行GetWindowText(hwndEdit ,szBuffer,100);后，szBuffer中没有内容。
#include <windows.h>
#include<stdio.h>LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
LRESULT CALLBACK ChildCardProc(HWND, UINT, WPARAM, LPARAM) ;TCHAR szChildClass[] = TEXT("card_child");
 
#define ID_BUTCARD   0
#define ID_CARDNEW   1
#define ID_TEXT      2
#define ID_EDIT      3
#define ID_BUTBACK   4
#define ID_BUTSAVE   5static HWND hwndcard;
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     static TCHAR szAppName[] = TEXT ("card") ;
     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) GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszMenuName  = NULL ;
     wndclass.lpszClassName = szAppName ;     if (!RegisterClass (&wndclass))
     {
          MessageBox (NULL, TEXT ("This program requires Windows NT!"), 
                      szAppName, MB_ICONERROR) ;
          return 0 ;
     }
     
 wndclass.lpfnWndProc   = ChildCardProc ;
// wndclass.cbWndExtra    = sizeof(long);
 wndclass.hIcon         = 0 ;
 wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszClassName = szChildClass ;  RegisterClass(&wndclass);
     hwnd = CreateWindow (szAppName,                  // window class name
                          TEXT ("申请"), // window caption
                          WS_OVERLAPPEDWINDOW,        // window style
                          CW_USEDEFAULT,              // initial x position
                          CW_USEDEFAULT,              // initial y position
                          400,              // initial x size
                          600,              // initial y size
                          NULL,                       // parent window handle
                          NULL,                       // window menu handle
                          hInstance,                  // program instance handle
                          NULL) ;                     // creation parameters
     
     ShowWindow (hwnd, iCmdShow) ;
     UpdateWindow (hwnd) ;
     
     while (GetMessage (&msg, NULL, 0, 0))
     {
          TranslateMessage (&msg) ;
          DispatchMessage (&msg) ;
     }
     return msg.wParam ;
}LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    

HDC         hdc ;
    PAINTSTRUCT ps ;
    HWND        cardnew;
     
     switch (message)
     {
     case WM_CREATE:
          hwndcard=CreateWindow(TEXT("button"),TEXT("新帐户"),
                    WS_CHILD|WS_VISIBLE|BS_PUSHBUTTON,
20,
20,
100,
30,
hwnd,
                                (HMENU)ID_BUTCARD,
((LPCREATESTRUCT)lParam)->hInstance,
NULL);
  return 0 ;  case WM_COMMAND:
  cardnew=CreateWindow(szChildClass,NULL, WS_CHILDWINDOW|WS_VISIBLE,
                 0,0,400,570,
 hwnd,
 (HMENU)ID_CARDNEW ,
 (HINSTANCE) GetWindowLong( hwnd,GWL_HINSTANCE),
 NULL);
  ShowWindow (hwndcard, SW_HIDE) ;
  return 0;
        
     case WM_PAINT:
          hdc = BeginPaint (hwnd, &ps) ;
 
          EndPaint (hwnd, &ps) ;
          return 0 ;
          
     case WM_DESTROY:
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}LRESULT CALLBACK ChildCardProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HDC                hdc;
PAINTSTRUCT        ps;
HWND               hwndText,hwndEdit,hButback;
static TCHAR       szBuffer[100];
int                iLength;
FILE               *fp; switch(message)
{
    case WM_CREATE:  
         hwndText = CreateWindow (TEXT ("static"), TEXT("姓名"),
                              WS_CHILD | WS_VISIBLE | SS_CENTER ,
                              20, 20, 
                              50, 20,
                              hwnd, (HMENU) ID_TEXT,
                              (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE),
                              NULL) ;   
 
 hwndEdit = CreateWindow (TEXT ("edit"), NULL,
                              WS_CHILD | WS_VISIBLE | WS_BORDER | ES_LEFT ,
                              100, 20, 
                              150, 20,
                              hwnd, (HMENU) ID_EDIT,
                              (HINSTANCE) GetWindowLong (hwnd, GWL_HINSTANCE),
                              NULL) ; 
     hButback=CreateWindow(TEXT("button"),TEXT("back"),
                   WS_CHILD|WS_VISIBLE|BS_PUSHBUTTON,
    300, 
540,
100,
30,
hwnd,
                                (HMENU) ID_BUTBACK,
((LPCREATESTRUCT)lParam)->hInstance,
NULL);         hButback=CreateWindow(TEXT("button"),TEXT("save"),
                   WS_CHILD|WS_VISIBLE|BS_PUSHBUTTON,
    0, 
540,
100,
30,
hwnd,
                                (HMENU) ID_BUTSAVE,
((LPCREATESTRUCT)lParam)->hInstance,
NULL);
         
 return 0;    case WM_COMMAND:
     switch(LOWORD(wParam))
{
 case ID_BUTSAVE:
                  GetWindowText(hwndEdit ,szBuffer,100);
  fp = fopen("E:\\STUDY\\WIN\\CARD\\card.dat","w+");
  fwrite(szBuffer,sizeof(szBuffer),1,fp);
  return 0;
            
 case ID_BUTBACK:
  ShowWindow(hwnd,SW_HIDE);
  ShowWindow(hwndcard,SW_SHOW);
  return 0;
       
}  return 0; case WM_PAINT:
     hdc=BeginPaint(hwnd,&ps);
  //  TextOut(hdc,100,100,szBuffer,iLength);
      // SetBkColor(hdc,COLOR_WINDOW);
     EndPaint(hwnd,&ps);
       return 0; }
return DefWindowProc(hwnd,message,wParam,lParam);}