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