Re: Passing c blocks to pre processor

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Sat, 28 May 2022, 06:49 Yair Lenga via Gcc, <gcc@gcc.gnu.org> wrote:

> Hi,
>
> I am trying to define macros that will accept code blocks. This will be
> used to create high level structures (like iterations, etc.). Ideally, I
> would like to do something like (this is simplified example, actual code
> much more application specific):
>
> Foreach(var, low, high, block)
>
> While should translate to:
> For (int var=low ; var < high ; var ++) block
>
> The challnge is the gcc pre processor does not accept blocks. It assume a
> comma terminate a block. For example:
> Foreach(foo, 1, 30, { int z=5, y=3, …}) will invoke the macro with 5
> arguments: (1) foo (2) 1, (3) 30, (4) { int z=5}, (5) y=3,
>
> Is there a way to tell CPP that an argument that start with ‘{‘ should
> extend until the matching ‘}’ ? Similar to the way ‘(‘ in macro arguments
> will extend till matching ‘)’.
>


This question seems off-topic on this mailing list, as it's not about GCC
development. It would be more suited to the gcc-help list.

I don't think you can do that. You need to use __VA_ARGS__ to accept
arbitrary code containing commas. You could look at how the
Boost.Preprocessor library works.