在点击div中的p时，如何阻止事件冒泡

 <div onclick="show('a')">
   <p onclick="show('b')"></p>
 </div>

div{
  width:500px;
  height:500px;
  background:red;
 }
 p{
  width:200px;
  height:200px;
  background:blue;
 }

 function show(info){
    alert(info);
 }

function show(e,info){
 function cancelBubble(e){
  e = e || window.event;
  if (e.stopPropagation) {  
     e.stopPropagation(); 
  }else {   
     e.cancelBubble = true; 
  } 
 }
 alert(info);
}

function show(info){
   alert(info);
   cancelBubble();
}
function cancelBubble(e) { 
   var evt = e ? e : window.event; 
    if (evt.stopPropagation) {  //W3C 
     evt.stopPropagation(); 
    }else {  //IE  
     evt.cancelBubble = true; 
    } 
}