Preprocessor macro that call another one : MSVC issue?

Question

I want to develop by myself a kind of for_each macro. I built it from scratch because I found other implementation in this website too much complicate and I do not find any resources on internet to learn tricks and tips about macros.

So, what I began to do is to make a make a macro that prints the square of a value. after I created a macro MAP that call MAP_ONE that calls f with the first arg.

On clang and gcc, this code works well :

#include <iostream>

using namespace std;

#define PRINT_SQUARE(x) std::cout << x * x << std::endl;

#define MAP(f, ...) MAP_ONE(f, __VA_ARGS__)

#define MAP_ONE(f, x, ...) f(x)

int main() {
  MAP(PRINT_SQUARE, 5, 8);
  return 0;
}

On MSVC it does not work. The errors are :

..\main.cpp(12): error C2563: mismatch in formal parameter list
..\main.cpp(12): error C2568: '<<': unable to resolve function overload
..\main.cpp(12): note: could be 'std::basic_ostream<_Elem,_Traits> &std::endl(std::basic_ostream<_Elem,_Traits> &)'

Is it a MSVC bug or is it normal and I just did something forbiden?

Thanks to the answer of Afshin, I modified the prior code to :

#include <iostream>

using namespace std;

#define PRINT_SQUARE(x) std::cout << ((x) * (x)) << std::endl;

#define MAP(f, ...) MAP_ONE(f, __VA_ARGS__)

#define MAP_ONE(f, x, ...) f(x) f(__VA_ARGS__)

int main() {
  MAP(PRINT_SQUARE, 5, 8);
  return 0;
}

On clang and GCC it prints : 25 and 64. On MSVC it does not compile :

D:\Desktop\Programmation\macro\main.cpp:12: error: C2059: syntax error: ')'

if you call `MAP_ONE` it works correctly. it is strange that with calling `MAP` it does not work. — Afshin, Dec 01 '18 at 19:10
It seems that for MSVC x is not equal to `5` but it is equal to `5, 8`, so it is evaluated to 8 * 8 = 64 — Antoine Morrier, Dec 01 '18 at 19:11

Afshin · Accepted Answer · 2018-12-01T20:06:49.757

1

UPDATE:

This solves the problem:

#include <iostream>

using namespace std;

#define EXPAND(x) x

#define PRINT_SQUARE(x) std::cout << x * x << std::endl;

#define MAP_ONE(f, x, ...) f(x)

#define MAP(f, ...) EXPAND(MAP_ONE(f, __VA_ARGS__ ))

int main() {
  MAP(PRINT_SQUARE, 5, 8);
  return 0;
}

Thanks to this link. It seems there is problem with expanding __VA_ARGS__ in VS and this trick will solve the problem.

edited Dec 01 '18 at 20:06

answered Dec 01 '18 at 19:04

Afshin

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It does not. It now compiles, but instead of printing 25, it prints 64... – Antoine Morrier Dec 01 '18 at 19:06
@AntoineMorrier yea I noticed too. – Afshin Dec 01 '18 at 19:09
Yeah that's true, I got this solution too. It seems that MSVC is too more compliant ahaha – Antoine Morrier Dec 01 '18 at 21:28
You need to use `/experimental:preprocessor` to use the latest preprocessor module of msvc – Antoine Morrier Dec 03 '18 at 20:51

Preprocessor macro that call another one : MSVC issue?

1 Answers1