关于钩子的使用，哟一点点的困惑！

if (g_hLogHook==NULL)
g_hLogHook = SetWindowsHookEx(WH_JOURNALRECORD,
(HOOKPROC)JournalLogProc,
HInstance,
0); //安装日志钩子
..............................................................
HOOKPROC JournalLogProc(int iCode,WPARAM wParam, LPARAM lParam)
{ //自定义的函数
if (iCode<0) //程序中没给iCode 赋值，他从什么地方传来的？
//是不是SetWindowsHookEx影响的？
return (HOOKPROC)CallNextHookEx(g_hLogHook,iCode,wParam,lParam);

if (iCode==HC_ACTION) //HC_ACTION在MSDN中找不到，什么意思？
{
//记录................
}
-----------------------------------------
附：CSDN CallNextHookEx
LRESULT CallNextHookEx(
HHOOK hhk, // handle to current hook
int nCode, // hook code passed to hook procedure
WPARAM wParam, // value passed to hook procedure
LPARAM lParam // value passed to hook procedure
);