I have a macro defined like this:
`define some_macro(ARG0, ARG1 = ARG0) \
...
I'd like the expansion some_macro(2) to expand to some_macro(2, 2). It expands to some_macro(2, ARG0), because in the default value specification for ARG1 the text ARG0 is used and not the value of the ARG0 argument.
Is it possible to specify the default of the second argument to be the value of ARG0?
Here's a good summary of what you can do with SV macros.
You could mostly achieve this with two macros, like
`define M(A1) \
`M2(A1, A1)
`define M2(A1, A2) \
"A1 A2"
module m();
initial begin
$display("joined string %s", `M(bye));
$finish;
end
endmodule
The difference is that this would require using either M or M2 depending on the number of arguments, not just one macro for both cases.
This can achieve the outcome you want. `ifdef ARG1 case is when a single argument is supplied, and `else is when both are. You can call another common macro there, I just wanted to demonstrate the trick to allow using the same macro name.
`define NOT_DEFINED
`define str2(ARG0, ARG1=NOT_DEFINED) \
`ifdef ARG1 \
`"ARG0 ARG0`" \
`else \
`"ARG0 ARG1`" \
`endif
module test;
initial begin
$display( `str2(hello) );
$display( `str2(hello, world) );
end
endmodule
Output:
hello hello
hello world
world to ARG1, I want to pass Tudor Timi. I'd end up with code like ifdef Tudor Timi, which I thought is illegal. Somehow, and don't ask me how, this seems to work. I had the impression that what comes after ifdef is limited to only be a single token, i.e. no spaces allowed. I also tried stuff like foo#(bar) (which can come up when trying to use types as macro arguments) and that also works! Mind blown!