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#define If_Helper_0(True)
#define If_Helper_1(True) True
#define If(Bit, True) If_Helper_ ## Bit (True)
 
#define Id2(Arg1, Arg2) Arg1, Arg2
 
int main()
{
	If(1, Id2(int a, b));
	a = b = 42;
}

prog.cpp:9:1: error: macro "If_Helper_1" passed 2 arguments, but takes just 1
  If(1, Id2(int a, b));
 ^
prog.cpp: In function ‘int main()’:
prog.cpp:3:23: error: ‘If_Helper_1’ was not declared in this scope
 #define If(Bit, True) If_Helper_ ## Bit (True)
                       ^
prog.cpp:9:2: note: in expansion of macro ‘If’
  If(1, Id2(int a, b));
  ^
prog.cpp:10:2: error: ‘a’ was not declared in this scope
  a = b = 42;
  ^
prog.cpp:10:6: error: ‘b’ was not declared in this scope
  a = b = 42;
      ^

Standard output is empty