What are PHP flags in function arguments?

Question

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?

possible duplicate of PHP function flags, how?

Quentin
– Quentin

2012-03-09 14:06:36 +00:00
Commented Mar 9, 2012 at 14:06 — Quentin
– Quentin, Commented Mar 9, 2012 at 14:06
Just var_dump() the cosntant, it'll show you the content.

MetalFrog
– MetalFrog

2012-03-09 14:07:27 +00:00
Commented Mar 9, 2012 at 14:07 — MetalFrog
– MetalFrog, Commented Mar 9, 2012 at 14:07

alex · Accepted Answer · 2012-03-09 14:35:50Z

14

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.

edited Mar 9, 2012 at 14:35

answered Mar 9, 2012 at 14:05

alex

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1 Comment

BoltClock Over a year ago

Also, these are called "bit flags".

bububaba · Accepted Answer · 2012-03-09 14:10:23Z

4

Usually flags are integers that are consecutive powers of 2, so that each has one bit set to 1 and all others to 0. This way you can pass many binary values in a single integer using bit-wise operators. See this for more (and probably more accurate) information.

answered Mar 9, 2012 at 14:10

bububaba

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