Difference between “include” and “require” in php

问题:

Is there any difference between them? Is using them a matter of preference? Does using one over the other produce any advantages? Which is better for security?

回答1:

You find the differences explained in the detailed PHP manual on the page of require:

require is identical to include except upon failure it will also produce a fatal E_COMPILE_ERROR level error. In other words, it will halt the script whereas include only emits a warning (E_WARNING) which allows the script to continue.

See @efritz\'s answer for an example

回答2:

require will throw a PHP Fatal Error if the file cannot be loaded. (Execution stops)

include produces a Warning if the file cannot be loaded. (Execution continues)

Here is a nice illustration of include and require difference:

From: Difference require vs. include php (by Robert; Nov 2012)

回答3:

Use include if you don\'t mind your script continuing without loading the file (in case it doesn\'t exist etc) and you can (although you shouldn\'t) live with a Warning error message being displayed.

Using require means your script will halt if it can\'t load the specified file, and throw a Fatal error.

回答4:

The key difference between require() and include() is that if you require() a file that can\'t be loaded (eg if it isn\'t there) then it generates a fatal error which will halt the execution of the page completely, and no more output will be generated. On the other hand, if you include() a file that can\'t be loaded, then this will merely generate a warning and continue building the page.

回答5:

As others pointed out, the only difference is that require throws a fatal error, and include - a catchable warning. As for which one to use, my advice is to stick to include. Why? because you can catch a warning and produce a meaningful feedback to end users. Consider

  // Example 1.
  // users see a standard php error message or a blank screen
  // depending on your display_errors setting
  require \'not_there\'; 


  // Example 2.
  // users see a meaningful error message
  try {
      include \'not_there\';
  } catch(Exception $e) {
     echo \"something strange happened!\";
  }

NB: for example 2 to work you need to install an errors-to-exceptions handler, as described here http://www.php.net/manual/en/class.errorexception.php

  function exception_error_handler($errno, $errstr, $errfile, $errline ) {
     throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
  }
  set_error_handler(\"exception_error_handler\");   

回答6:

<?PHP
echo \"Firstline\";
include(\'classes/connection.php\');
echo \"I will run if include but not on Require\";
?>

A very simple Practical example with code. The first echo will be displayed. No matter you use include or require because its runs before include or required.

To check the result, In second line of a code intentionally provide the wrong path to the file or make error in file name. Thus the second echo to be displayed or not will be totally dependent on whether you use require or include.

If you use require the second echo will not execute but if you use include not matter what error comes you will see the result of second echo too.

回答7:

In case of Include Program will not terminate and display warning on browser,On the other hand Require program will terminate and display fatal error in case of file not found.