wstring转string wstring转char*

wstring转换为string
wstring wstr=_T("你猜你猜"); 
int size=WideCharToMultiByte(CP_ACP,0,wstr.c_str(),-1,NULL,0,NULL,NULL); 
char *ch=new char[size+1]; 
if(!WideCharToMultiByte(CP_ACP,0,wstr.c_str(),-1,ch,size,NULL,NULL)) 
{ 
    return false; 
} 

string str=ch;