Flags, enum (C)
You should make the flags only powers of two, i.e. each is a bit in whatever data type you're storing this in, and nothing overlaps when you bitwise OR.
another way of storing flags is to not bother with the underlying type at all. when using an enum, the enum values are stored by default into an unsigned int, which is 32 bits on a common computer. this gives you with only 32 possible flags: while certainly much, there are some cases where it is not sufficient.
now you can define your flag set this way:
typedef struct
{
int takes_damage : 1;
int grabbable : 1;
int liquid : 1;
int some_other : 1;
} flags;
if you never encountered this, the ': 1' part tells the compiler to only use 1 bit to store this struct member.
now you can define a variable to hold the flags, and work with those flags:
flags myflags = {1,0,0,1}; // defines a variable holding a set of flags, with an initial value of takes_damage & some_other
myflags.liquid = 1; // change the flags to include the liquid
if ( myflags.takes_damage ) // test for one flag
apply_damage();
if ( myflags.liquid && myflags.some_other ) // test for multiple flags
show_strange_behavior();
this method allows you to define any number of flags, without limitation, and you can extend your flag set at any time without fearing an overflow. the drawback is that testing a subset of the flags is more cumbersome and necessitate more code.
Yes. Instead, make your enum members powers of 2:
enum
{
TAKES_DAMAGE = (1 << 0),
GRABBABLE = (1 << 1),
LIQUID = (1 << 2),
SOME_OTHER = (1 << 3)
};
Your enumeration needs to be powers of two :
enum
{
TAKES_DAMAGE = 1,
GRABBABLE = 2,
LIQUID = 4,
SOME_OTHER = 8
};
Or in a more readable fashion :
enum
{
TAKES_DAMAGE = 1 << 0,
GRABBABLE = 1 << 1,
LIQUID = 1 << 2,
SOME_OTHER = 1 << 3
};
Why ? Because you want to be able to combine flags with no overlapping, and also be able to do this:
if(myVar & GRABBABLE)
{
// grabbable code
}
... Which works if the enumeration values look like this :
TAKES_DAMAGE: 00000001
GRABBABLE: 00000010
LIQUID: 00000100
SOME_OTHER: 00001000
So, say you've set myVar
to GRABBABLE | TAKES_DAMAGE
, here's how it works when you need to check for the GRABBABLE flag:
myVar: 00000011
GRABBABLE: 00000010 [AND]
-------------------
00000010 // non-zero => converts to true
If you'd set myVar
to LIQUID | SOME_OTHER
, the operation would have resulted in :
myVar: 00001100
GRABBABLE: 00000010 [AND]
-------------------
00000000 // zero => converts to false