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A. Cedano
Asked: 2020-05-03 02:58:30 +0800 CST 2020-05-03 02:58:30 +0800 CST

What is the difference between require, require_once, include, include_once in PHP?

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In PHP there are several ways to add files into others using:

  • require()
  • require_once()
  • include()
  • include_once()

But is there any difference between them?

Are there specific cases where it is better to use one or the other?

The objective of the question is to have a clear idea about whether in some cases it is convenient to use one or the other, to have a more optimized code taking into account the consumption of resources or other criteria, for this reason, it is convenient that in the answer it is indicated if the use of one or the other affects to a greater or lesser degree the amount of memory that is consumed or other important details.

php

2 Answers

  1. Best Answer

    include

    inserts a code from another file into our program, in case said file does not exist or has errors inside, our program will show a warning but it will continue to work .

    require

    It works similarly to include, but in this case, if the file does not exist or contains errors, our program will not work and we will get a fatal error in the log .

    Include_once and Require_once

    They work exactly the same way as the previous ones, except that they prevent the loading of the same file several times.

    Final conclusion:

    We can think of using include when the file to be inserted is not decisive regarding the operation of our program. Require when said file is necessary for the correct functioning of our program.

    Finally, the variants with _once should be used when our program has considerable dimensions and it may be the case that the inclusion of the file occurs several times. These last variants must be used only in exceptional cases since they consume more resources than the previous ones.

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  2. According to the official PHP documentation :

    requireis identical to includeexcept that on failure it will produce a fatal error of level E_COMPILE_ERROR. In other words, it stops the script while include will just issue a warning ( E_WARNING) which allows the script to continue.

    The statement require_onceis identical to requireexcept that PHP will check to see if the file has already been included, and if so, it doesn't include ( require) again.

    The statement include_onceincludes and evaluates the specified file during script execution. It has a behavior similar to that of the statement include, the only difference being that if the code of the file has already been included, it will not be included again, and it include_oncewill return TRUE. As its name indicates, the file will be included only once.

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