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分享//截取TextOut
typedef UINT (WINAPI* ALLOCCSTODSALIAS)(UINT);
ALLOCCSTODSALIAS AllocCsToDsAlias;
BYTE NewValue[5];//保存新的入口代码
BYTE OldValue[5];//API原来的入口代码
unsigned char * Address=NULL;//可写的API入口地址
UINT DsSelector=NULL;//指向API入口的可写的选择符
WORD OffSetEntry=NULL;//API的偏移量
BOOL bHookAlready = FALSE; //是否挂钩子的标志
BOOL InitHook()
{
HMODULE hKernel,hGdi;
hKernel = GetModuleHandle("Kernel");
if(hKernel==NULL)
return FALSE;
AllocCsToDsAlias = (ALLOCCSTODSALIAS)GetProcAddress(hKernel,"AllocCsToDsAlias");//这是未公开的API所以要这样取地址
if(AllocCsToDsAlias==NULL)
return FALSE;
hGdi = GetModuleHandle("Gdi");
if(hmGdi==NULL)
return FALSE;
FARPROC Entry = GetProcAddress(hGdi,"TextOut");
if(Entry==NULL)
return FALSE;
OffSetEntry = (WORD)(FP_OFF(Entry));//取得API代码段的选择符
DsSelector = AllocCsToDsAlias(FP_SEG(Entry));//分配一个等同的可写的选择符
Address = (unsigned char*)MK_FP(DsSelector,OffSetEntry);//合成地址
NewValue[0]=0xEA;
*((DWORD*)(NewValue+1)) = (DWORD)MyTextOut;
OldValue[0]=Address[0];
*((DWORD*)(OldValue+1)) = *((DWORD*)(Address+1));
}
BOOL ClearHook()
{
if(bHookAlready)
HookOff();
FreeSelector(DsSelector);
}
BOOL HookOn()
{
if(!bHookAlready){
for(int i=0;i<5;i++){
Address[i]=NewValue[i];
}
bHookAlready=TRUE;
}
}
BOOL HookOff()
{
if(bHookAlready){
for(int i=0;i<5;i++){
Address[i]=OldValue[i];
}
bHookAlready=FALSE;
}
}
//钩子函数,一定要和API有相同的参数和声明
BOOL WINAPI MyTextOut(HDC hdc,int nXStart,int nYStart,LPCSTR lpszString,UINT cbString)
{
BOOL ret;
HookOff();
ret = TextOut(hdc,nXStart,nYStart,lpszString,cbString);//调原来的TextOut
HookOn();
return ret;
}