How does PHP read dat files?

How does PHP read dat files? How does PHP read two dat files, two data files, one storage name and one data access file ?, First of all, we need to know how the data is organized, first of all, we need to know how the data is organized, look at the php documentation, the best http://php.net, fopen is the same as txt? How does PHP read dat files?
How to read two dat files, two data files are associated, one storage name and one data access?

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First, you must know how data is organized.
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Discussion
First, you must know how data is organized.

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It's best to read the php document.

Http://php.net
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Is fopen the same as txt?