What is the "(x)" term in macro-CodePudding

I found a structure definition as shown below,

#define MAX_SIZE(x) 1

struct var
{

    int temp;
    int temp2[MAX_SIZE(temp)];

};

What does MAX_SIZE(temp) mean?.

What is the dimension of temp2 array?.

CodePudding user response：

I suspect the intention here is to document which field of the structure governs the actual size of a flexible array member. Since C provides no way to tell the compiler the actual size of a flexible array member, it's intentional that MAX_SIZE ignores its argument, because the C compiler can't make any use of the information. It's just for human readers. (This should have been explained in documentation comments above the definition of MAX_SIZE.)

Whoever wrote the code is confusing the issue by using the really old notation for flexible array members: neither the C99 sanctioned syntax temp2[] nor the older GNU extension temp2[0], but the way you wrote it in the days of pcc, temp2[1]. Are you looking at the source code to a very old program? Is it still using old-style function definitions perchance?

Anyway, you should understand the definition of struct var as being

struct var
{
    int temp;
    int temp2[temp];
};

... in the counterfactual version of C in which you can actually write that, of course.

CodePudding user response：

If you are curious what the preprocessor is doing, your compiler can generate the preprocessed file for you. For example, compile this with gcc -E try.c -o try.i and take a look at the output.

This fragment is small enough you can just do gcc -E try.c, but in general if you include anything the preprocessed output can get quite long.

This macro is pretty useless: anything you give it resolves to 1