Why use apparently meaningless do-while and if-else statements in macros?

Question

In many C/C++ macros I'm seeing the code of the macro wrapped in what seems like a meaningless `do while` loop. Here are examples. #define FOO(X) do { f(X); g(X); } while (0) #define FOO(X) if (1) { f(X); g(X); } elseI can't see what the `do while` is doing. Why not just write this without it? #define FOO(X) f(X); g(X)

Answer 1

My best guess is that it's just remnant debugging code.

Sometimes when I'm working on something and want to test some functionality, instead of commenting out an if statement, I can simply set it to "if(false)" so that it's guaranteed to skip it. Or vice versa if I want to test out logic inside of an if block, but don't want to have to do a bunch of setup in order for it the evaluate as true, so I can just hard code it to true to force it to enter.

Looks like that may have been what was going on with this macro, and whoever designed it just never went through to do cleanup.