I founs this code in w3schoool javascript coookie section, which is to read the cookie:

function getCookie(c_name)
{
if (document.cookie.length>0)
  {
  c_start=document.cookie.indexOf(c_name + "=");
  if (c_start!=-1)
    {
    c_start=c_start + c_name.length+1;
    c_end=document.cookie.indexOf(";",c_start);
    if (c_end==-1) c_end=document.cookie.length;
    return unescape(document.cookie.substring(c_start,c_end));
    }
  }
return "";
}

In this line:

if (document.cookie.length>0)

what mean document.cookie.length?

In this line:

c_start=document.cookie.indexOf(c_name + "=");

why i need to add '=' after the c_name(cookie name)

In this line:

c_start=c_start + c_name.length+1;

why I need to add c_name.length+1 ? What the purpose?

And what the meaning of this line:

  if (c_end==-1) c_end=document.cookie.length;

Can Anyone answer my question?Thanks!!!