What are PHP flags in function arguments?

php function flags
enchance picture enchance · Mar 9, 2012 · Viewed 10.9k times · Source

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?

Answer

alex picture alex · Mar 9, 2012

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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