在ajax中动态创建的文本框返回null

Question

Following is the code in which textbox is created

<input type="text" class="enter_comment"  value='comments' id='comm<?php echo $row['p_id'];?>'/>
<input type='button' value='enter' class='cbtn' id='<?php echo $row['p_id'];?>'>

And here is the button click code in ajax.

$(".cbtn").click(
    function(e){
        alert("here");
        var id=$(this).attr('id');
        var c="#comm"+id;   

        var comment = $(c).attr("value");
        event.stopImmediatePropagation();

        $.post("comments.php",{id:id, comment:comment},function(e){         
            $('.comment').append(e);
        }       
    );      
});

The problem is that when I try to get value of text box , it returns null. Even when I tried to set value through innerHTML, it said : "Cannot set property of null".

Above mentioned code is in AJAX in the same file. And ids of text boxes are set by value in database