Creating a digit Datatype with restriction, an int between -10 and 10

Question

I really need a new datatype in my application, which will only store numbers from -10 to 10. Is there a way to create a datatype with specific values, which will raise an error if the value is invalid? I used:

typedef int digit;

The thing that happens is a new datatype which is actually int is created. I also tried this:

typedef int{-10 > int value < 10} digit;

but it raised this:

exit status 1
main.cpp:3:12: error: expected unqualified-id before '{' token
typedef int{-10 > int value < 10} digit;
           ^
main.cpp:3:35: error: 'digit' does not name a type; did you mean 'div_t'?
typedef int{-10 > int value < 10} digit;
                                    ^~~~~
                                  div_t

C++ is not ADA. It's not possible with fundamental types.. You can write a class to handle the datatype. You can overload most operators, thus handle overflows in custom ways. — KamilCuk, Jan 14 '19 at 10:57

score 1 · Accepted Answer · answered Jan 14 '19 at 11:01

1

C++ does not have such a feature. It would be quite nice in certain situations, but non-trivial to provide in the language (and inefficient to use, to some degree).

You can create a class that wraps int and does its own bounds checking (or however you want the type to behave). You would then have to wrap all the arithmetic operations too. Not too onerous, but a bit of a pain in the neck. And, again, not efficient (every single arithmetic operation will need a branch!).

Generally we just use an int and do our checks in our code logic when needed, at a higher level. I can't make specific suggestions without knowing your use case.

Here's an example that does half of it.

answered Jan 14 '19 at 11:01

Lightness Races in Orbit

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Thanks, that works – Andrii Chumakov Jan 14 '19 at 11:05
@AndriiChumakov It doesn't do everything you seem to want; it only validates the initial value – Lightness Races in Orbit Jan 14 '19 at 11:06
I understand, that I will be able to attach a new value with a bigger number like 11, because this code checks the value of a number only before the assignment. – Andrii Chumakov Jan 14 '19 at 11:16
@AndriiChumakov Not quite - the only way to obtain the value is, well, by value, and involves a conversion back to `int`, so the range-checked type is effectively immutable. Converting it back to that type you'd get another range check. This may or may not be suitable for your purposes. – Lightness Races in Orbit Jan 14 '19 at 11:17
ok, I will check if it will be useful – Andrii Chumakov Jan 14 '19 at 11:18
@AndriiChumakov Good luck! – Lightness Races in Orbit Jan 14 '19 at 11:22
Found another duplicate with more possible solutions - you should have plenty of options now. – Useless Jan 14 '19 at 12:58
@Useless That's pretty good, nice work. ("Found" seems like an overstatement since you wrote the best answer there :P) – Lightness Races in Orbit Jan 14 '19 at 13:00
"Found somewhere in the back of my mind," perhaps :) – Useless Jan 14 '19 at 13:03

Creating a digit Datatype with restriction, an int between -10 and 10

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