[SOLVED] Is it OK to use a code block as an argument for a C macro?

Is it OK to use a code block as an argument for a C macro?

I have a pattern that is basically some boilerplate code with a part that varies in the middle

if(condition){
    struct Foo m = start_stuff();
    { m.foo = bar(1,2); m.baz = 17; } //this part varies
    end_stuff();
}

Is it OK to make a macro taht takes that intermediate code block as an argument? The rules for macro expansion in C seem awfully complicated so I am not sure if there aren't any corner cases that could come and bite me in the future (in particular, I don't understand how the macro arguments are separated if my code has commas in it).

#define MY_MACRO(typ, do_stuff) do { \
    if(condition){ \
        struct typ m = start_stuff(); \
        do_stuff; \
        end_stuff(); \
    } \
}while(0)

//usage
MY_MACRO(Foo, {
   m.foo = bar(1,2);
   m.baz = 17;
});

So far the only thing that I managed to think of is break and continue getting captured if I use looping statements in my macro and that would be an acceptable tradeoff for my particular use case.

edit: Of course, I would have used a functions if I could. The example I used in this question is simplified and doesn't showcase the bits that can only work with macro magic.

Solution

You can put a code block into a macro argument provided that it has no unguarded comma. In your example, the only comma in the argument is guarded because it is surrounded by parentheses.

Note that only parentheses guard commas. Brackets ([]) and braces ({}) do not. (And neither do angle brackets (<>) as noted in a comment.)

However, if the code block argument is the macro's last argument, you can use a variadic macro to increase flexibility. But beware: the increased flexibility also means that errors might go unnoticed. If you do this, you'll only have to make sure that the parentheses are balanced. (Again, only parentheses matter to the macro processor.)