Flag

A Flag is a boolean value that is stored in an integer variable.

Flags are stored together within an integer instead of a boolean for each flag because the smallest amount of memory that a program can access is a byte. If you used a boolean for the flags you'd be using a whole byte (8 bits) when all you need is 1 bit. An integer contains 32 bits. By placing the flags within an integer it means that the space is used much more efficiently than if you used a lot of booleans. Up to 32 individual flags can be stored in a single int, since each is represented by one of its bits.

Creation

Flags are created like this:

#define FL_MYFLAG 1<<0
#define FL_MYFLAG 1<<1
#define FL_MYFLAG 1<<2
etc.

Or sometimes like this (e.g. spawnflags):

#define FL_MYFLAG 1
#define FL_MYFLAG 16
#define FL_MYFLAG 32
etc.

You can then use the #defs in place of the numbers.

Usage

Flags are managed through functions, never directly. There are several different types of flags and each has its own set, but they all follow the same naming pattern:

• Add<*>Flags()
• Remove<*>Flags()
• Clear<*>Flags()
• Has<*>Flags() (sometimes Is<*>FlagSet())

To operate on several flags at once you must use the bitwise operators &, | and ^ - the same as the normal boolean operators, but with only one character.

For instance:

if ( HasSpawnFlags(SF_CITIZEN_MEDIC | SF_CITIZEN_NOT_COMMANDABLE) )
	...

Flags in Hammer Editor

Flags appear in object properties in Valve Hammer Editor. Different objects will have different flags available. A flag appears as a checkbox, meaning each flag can be either on or off.