何时找不到网址时出现错误消息

I want to call a file by an url. If the url is not found then I want to show an error message instead of showing "The requested url is not found". How I will do this? Please help me.

Create a .htaccess file in your web directory, and write the following:

ErrorDocument 404 /notfound.html

Make sure to replace notfound.html with your custom 404 html file.

$headers=get_headers($url);

Then check if $result[0] contains 200 OK (which means the file is there)

A function to check if a URL works could be this:

function UR_exists($url)
{
   $headers=get_headers($url);
   return stripos($headers[0],"200 OK")?true:false;
}

/* You can test a URL like this (sample) */

if(UR_exists("https://www.example.com/"))
   echo "This page exists";
else
   echo "This page does not exist";

Hope this will help you out.