enum arithmetic by the preprocessor

[mmesser]

We have a bunch of enum values in our code. We need a string in the string table for each one.

MyFile.h

enum FOO
{
    FOO_BASE = 0,
    FOO_1,
    FOO_2,

    FOO_MAX
};

resource.h

#define IDS_BAR_BASE  4096
#define IDS_BAR_1     4097
#define IDS_BAR_2     4098
#define IDS_BAR_MAX   4099

I am trying to create a sanity check in case more FOO's or BAR's are added.

MyFile.cpp

#if ((FOO_MAX - FOO_BASE) != (BAR_MAX - IDS_BAR_BASE))
    #error Each FOO in Myfile.h must have its corresponding BAR string in resource.h. 
#endif

This does not work. The #if evaluates TRUE, the #error is compiled, and I get an error.

A little experimentation shows that the preprocessor is evaluating FOO_MAX as 0.

I have tried a few variations on this, such as ((int)FOO_MAX). Nothing works.

What is wrong? How do I fix it?

[cilu]

A little experimentation shows that the preprocessor is evaluating FOO_MAX as 0.

Of course it does since it does not evaluate it at all. The preprocessor evaluates macros and preprocesor directives only. The compiler is the one that evaluates the enumerations. So, your solution is doomed to fail.

[mmesser]

You are right. It took me a while to see that.

The development environment does evaluate it if you hold the mouse over it. I was thinking the preprocessor did the same. My bad.

I will make it an ASSERT.

[cilu]

The development environment does evaluate it if you hold the mouse over it. I was thinking the preprocessor did the same. My bad.

That's the IntelliSense working there. It builds a database with information about your types, variables, functions, etc. by analyzing the code. It is keep it in a file with the extension .ncb.