optimization - Specifying size of enum type in C

Question

Already read through this related question, but was looking for something a little more specific.

• Is there a way to tell your compiler specifically how wide you want your enum to be?
• If so, how do you do it? I know how to specify it in C#; is it similarly done in C?
• Would it even be worth doing? When the enum value is passed to a function, will it be passed as an int-sized value regardless?

question from:https://stackoverflow.com/questions/4879286/specifying-size-of-enum-type-in-c

Answer 1

Is there a way to tell your compiler specifically how wide you want your enum to be?

In general case no. Not in standard C.

Would it even be worth doing?

It depends on the context. If you are talking about passing parameters to functions, then no, it is not worth doing (see below). If it is about saving memory when building aggregates from enum types, then it might be worth doing. However, in C you can simply use a suitably-sized integer type instead of enum type in aggregates. In C (as opposed to C++) enum types and integer types are almost always interchangeable.

When the enum value is passed to a function, will it be passed as an int-sized value regardless?

Many (most) compilers these days pass all parameters as values of natural word size for the given hardware platform. For example, on a 64-bit platform many compilers will pass all parameters as 64-bit values, regardless of their actual size, even if type int has 32 bits in it on that platform (so, it is not generally passed as "int-sized" value on such a platform). For this reason, it makes no sense to try to optimize enum sizes for parameter passing purposes.