请教《windows程序设计》里的一个问题

请教《windows程序设计》里的一个问题
本书第四章的例题SYSMETS1.c里有一行：#define WINVER 0X0500  什么意思？
没有他为什么通不过编译？请指教，谢谢！！
代码如下：
//SYSMETS.H #define NUMLINES ((int) (sizeof sysmetrics / sizeof sysmetrics [0]))struct
{
     int     iIndex ;
     TCHAR * szLabel ;
     TCHAR * szDesc ;
}
sysmetrics [] =
{
     SM_CXSCREEN,             TEXT ("SM_CXSCREEN"),              
                              TEXT ("Screen width in pixels"),
     SM_CYSCREEN,             TEXT ("SM_CYSCREEN"),              
                              TEXT ("Screen height in pixels"),
     SM_CXVSCROLL,            TEXT ("SM_CXVSCROLL"),             
                              TEXT ("Vertical scroll width"),
     SM_CYHSCROLL,            TEXT ("SM_CYHSCROLL"),             
                              TEXT ("Horizontal scroll height"),
     SM_CYCAPTION,            TEXT ("SM_CYCAPTION"),             
                              TEXT ("Caption bar height"),
     SM_CXBORDER,             TEXT ("SM_CXBORDER"),              
                              TEXT ("Window border width"),
     SM_CYBORDER,             TEXT ("SM_CYBORDER"),              
                              TEXT ("Window border height"),
     SM_CXFIXEDFRAME,         TEXT ("SM_CXFIXEDFRAME"),          
                              TEXT ("Dialog window frame width"),
     //未写完......
} ;//SYSMETS1.c#define WINVER 0x0500  //这行什么意思？没有他通不过编译...
#include<windows.h>
#include"sysmets.h"LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,
   PSTR szCmdLine,int iCmdShow)
{
static TCHAR szAppName[]=TEXT("SysMets1");
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;
} hwnd=CreateWindow(szAppName,TEXT("Get System Metrics No.1"),
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;
}LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam)
{
static int cxChar,cxCaps,cyChar;
HDC hdc;
int i;
PAINTSTRUCT ps;
TCHAR szBuffer[10];
TEXTMETRIC tm; switch(message)
{
case WM_CREATE:
hdc=GetDC(hwnd);
GetTextMetrics(hdc,&tm);
cxChar=tm.tmAveCharWidth;
cxCaps=(tm.tmPitchAndFamily &1?3:2)*cxChar/2;
cyChar=tm.tmHeight+tm.tmExternalLeading; ReleaseDC(hwnd,hdc);
return 0;
case WM_PAINT:
hdc=BeginPaint(hwnd,&ps);
for(i=0;i<NUMLINES;i++)
{
TextOut(hdc,0,cyChar *i,
sysmetrics[i].szLabel,
lstrlen(sysmetrics[i].szLabel));
TextOut(hdc,22 * cxCaps,cyChar * i,
sysmetrics[i].szDesc,lstrlen(sysmetrics[i].szDesc));
SetTextAlign(hdc,TA_RIGHT|TA_TOP);
TextOut(hdc,22 * cxCaps+40 * cxChar,cyChar * i,szBuffer,
wsprintf(szBuffer,TEXT("%5d"),GetSystemMetrics(sysmetrics[i].iIndex)));
SetTextAlign(hdc,TA_LEFT|TA_TOP);
}
EndPaint(hwnd,&ps);
return 0;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd,message,wParam,lParam);
}