div三列宽度自适应结构实现代码

#main{
width:760px;
margin:0 auto;
}
.left{
width:100px;
float:left;
}
.right{
width:120px;
float:right;
}
.center{
margin:0 120px 0 100px;
width:auto;
}
.clear{clear: both;}

<!--注意：center这个div的位置-->
<div id="main">
<div class="left"></div>
<div class="right"></div>
<div class="center"></div>
<div class="clear"></div>
</div>