C++ the operator ## don't work with a string and a macro

Question

The ## are not working with an string an a macro. My compiler not extract the value of the macro or something else after ##

#define ProfilerScope(name) Timer timer ## __LINE__;

This just returns me Timer timer__LINE__

I tried to make a STRINGIZE macro to makes this works but nothing, they just returns me the same

#define STRINGIZE(x) STRINGIZE_SIMPLE(x)
#define STRINGIZE_SIMPLE(x) #x

#define ProfilerScope(name) Timer timer ## STRINGIZE(__LINE__);

return Timer timerSTRINGIZE(__LINE__)

I want it to return the line of code where I'm using the macro

`STRINGIZE` adds quotes, and `Timer timer42;` is supposed to have no quotes. But notice how `STRINGIZE` uses two macros instead of one. You must do the same: pass `__LINE__` from one macro to another, then use `##` in the second macro. — HolyBlackCat, Jan 22 '23 at 13:28
`##` operator applies after parameter substitution but before the list is reprocessed for further macro replacements. You need a couple levels of indirection, with `##` at the very end. [Something like this](https://godbolt.org/z/9hqcbM1cf) — Igor Tandetnik, Jan 22 '23 at 13:29

score 0 · Accepted Answer · answered Jan 24 '23 at 08:50

I want it to return the line of code where I'm using the macro

I think you want to expand __LINE__ and then concatenate it with a word. You have to expand it in a macro. The following code:

#define CONCAT(a, b)  CONCAT2(a, b)
#define CONCAT2(a, b)  a##b
#define ProfilerScope(name) Timer CONCAT(timer, __LINE__);
ProfilerScope()

outputs Timer timer4;.

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