What is the difference between php include and include_once

When we use PHP to write web pages, sometimes we need to include code in other PHP files in the current PHP file. At this time, you can use the include or include_once function to implement file inclusion.

So, what is the difference between include and include_once?

First let’s understand the functions of these two functions:

include The function can include specified files in the current PHP file, and include_once The function can also include the specified file in the current PHP file, but it will only take effect when the file is included in the current PHP file for the first time. It will not take effect if it is included again later.

Let’s take a look at their usage separately:

include Function usage:

include 'file.php';

Among them, file.php is the file name that needs to be included.

include_once Function usage:

include_once 'file.php';

Similarly, file.php is the name of the file that needs to be included.

From a usage point of view, the main difference between them is that include_once means to include it only once. No matter how many times the file is included, it will only be included once.

So, which function is better to use?

Generally, if we need to include the same file multiple times, we should use the include function; if we need to include the same file multiple times in different PHP files, we should Use the include_once function. This can effectively improve code execution efficiency and avoid code conflicts.

Finally, one thing to note is that when including files, the file name should use an absolute path or a relative path, depending on the actual situation.

In short, the include and include_once functions are widely used. Mastering their differences and correct usage can allow us to better write efficient and Maintainable PHP code.

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