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Asked: 2026-05-31T00:44:55+00:00

I noticed that some functions in PHP use flags as arguments. What makes them

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I noticed that some functions in PHP use flags as arguments. What makes them unique instead of plain string arguments? I’m asking since I want to use them on my own custom functions but am curious as to what the process is for doing so.

Edit: TO summarize, when is it best to create a custom function with flags and when is it not?

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  1. Editorial Team

    They are just constants which map to a number, e.g. SORT_NUMERIC (a constant used by sorting functions) is the integer 1.

    Check out the examples for json_encode().

    As you can see, each flag is 2n. This way, | can be used to specify multiple flags.

    For example, suppose you want to use the flag JSON_FORCE_OBJECT (16 or 00010000) and JSON_PRETTY_PRINT (128 or 10000000).

    The bitwise operator OR (|) will turn the bit on if either operand’s bit is on…

    JSON_FORCE_OBJECT | JSON_PRETTY_PRINT

    …is internally….

    00010000 | 1000000

    …which is…

    10010000

    You can check it with…

    var_dump(base_convert(JSON_PRETTY_PRINT | JSON_FORCE_OBJECT, 10, 2));
// string(8) "10010000"

    CodePad.

    This is how both flags can be set with bitwise operators.

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