#define ON_MEAL_PLAN 1
#define ON_HOUSING_PLAN 2
#define ON_PARKING_PLAN 4
#define ON_FINANCIAL_PLAN 8
#define by orders of two in a clean fashion
Author
I'm doing some stuff with bit operations in C++, and I need to #define constants by orders of two. For example, say I had a char variable representing financial packages for students at college. They can be on a meal plan, a housing plan, a parking space plan, and/or a financial aid plan. If I want to store whether they are on these plans, I might #define them like this:
You mean something like this?
EDIT: Err, this may look a bit better:
enum { ON_MEAL_PLAN = 1, ON_HOUSING_PLAN = 2 << 0, ON_PARKING_PLAN = 2 << 1, ON_FINANCIAL_PLAN = 2 << 2};EDIT: Err, this may look a bit better:
enum { ON_MEAL_PLAN = 1 << 0, ON_HOUSING_PLAN = 1 << 1, ON_PARKING_PLAN = 1 << 2, ON_FINANCIAL_PLAN = 1 << 3};
Author
Sure, I think that would work fine! Unless anyone else thinks of a nicer-looking way, I'll just go with that. Thanks.
Quote:Original post by silverphyre673
I'm doing some stuff with bit operations in C++, and I need to #define constants by orders of two. For example, say I had a char variable representing financial packages for students at college. They can be on a meal plan, a housing plan, a parking space plan, and/or a financial aid plan. If I want to store whether they are on these plans, I might #define them like this:#define ON_MEAL_PLAN 1#define ON_HOUSING_PLAN 2#define ON_PARKING_PLAN 4#define ON_FINANCIAL_PLAN 8
I would really rather #define these by orders of two; this is really just kind of a code formatting issue... I want it to look nice :) Any ideas? If you don't understand me, just ask and I'll try to clarify.
One relatively common thing is to bit shift each one
#define ON_MEAL_PLAN (1<<0)#define ON_HOUSING_PLAN (1<<1)#define ON_PARKING_PLAN (1<<2)#define ON_FINANCIAL_PLAN (1<<3)#define ON_MEAL_PLAN 1#define ON_HOUSING_PLAN 2#define ON_PARKING_PLAN 4#define ON_FINANCIAL_PLAN 8
Author
OK. Yeah, this is a total formatting issue, so I think the enumeration bit-shifting technique will work fine. I remember seeing this somewhere months ago online, but I'd forgotten. Thanks, all!
you could always just make a set of standard defs
#define BIT1 (1<<0)
#define BIT2 (1<<1)
...
or
#define BIT(x) (1<<x)
and then just do
#define ON_MEAL_PLAN BIT(1)
#define ON_HOUSING_PLAN BIT(2)
...
#define BIT1 (1<<0)
#define BIT2 (1<<1)
...
or
#define BIT(x) (1<<x)
and then just do
#define ON_MEAL_PLAN BIT(1)
#define ON_HOUSING_PLAN BIT(2)
...
You usually see it as hex
enum MyEnum {
A = 0x01,
B = 0x02,
C = 0x04,
D = 0x08,
E = 0x10,
F = 0x20,
G = 0x40,
H = 0x80,
I = 0x100
}
Or bit-fields might be what you really want:
struct Stuff {
uint32 MealPlan :1;
uint32 HousingPlan :1;
uint32 ParkingPlan :1;
uint32 FinancialPlan :1;
};
unsigned bit-fields are technically non-standard, but I never see signed bit-fields in code.
enum MyEnum {
A = 0x01,
B = 0x02,
C = 0x04,
D = 0x08,
E = 0x10,
F = 0x20,
G = 0x40,
H = 0x80,
I = 0x100
}
Or bit-fields might be what you really want:
struct Stuff {
uint32 MealPlan :1;
uint32 HousingPlan :1;
uint32 ParkingPlan :1;
uint32 FinancialPlan :1;
};
unsigned bit-fields are technically non-standard, but I never see signed bit-fields in code.
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