compile error when using parenthesis in visual studio but pass in g++/clang++

Question

I am developing cross-platform project, and I found something strange. in visual studio, the following code will fail. But g++/clang++ in Linux environment can compile without error. In addition, I search for keyword on VS, but found nothing. Anyone the reason?

int main(){
  ({;});
  return 0;
}

error C2059: syntax error: '{'
error C2143: syntax error: missing ';' before '{'
error C2059: syntax error: ')'

Visual Studio version I have : Microsoft Visual Studio Professional 2019, Version 16.5.1

@JaMiT I think that's what I need, thanks! – CY.Lee May 13 '20 at 09:51 — CY.Lee, May 13 '20 at 09:51

score 0 · Answer 1 · answered May 13 '20 at 03:58

0

In visual studio, it is interpreted as vc++. In c++, ; marks end of statement. So your code ({;}); is exactly taken by compiler as 1 ({; and 2 }); as a statement which is synaxtically not correct. Check syntax of wrting code in c++. I dont know about g++/clang. Sorry there.

answered May 13 '20 at 03:58

user9559196

157
6

By your theory `for(;;)` should be illegal, except it's not. – dxiv May 13 '20 at 04:02
No, that is syntaxically correct – user9559196 May 13 '20 at 04:31

obataku · Answer 2 · 2020-05-13T04:15:29.987

Compiling with clang++ using the -pedantic -Werror flags we see

dummy.cc:2:4: error: use of GNU statement expression extension [-Werror,-Wgnu-statement-expression]
  ({;});
   ^
1 error generated.

The MSVC compiler (cl, typically used by Visual Studio) does not support many non-standard extensions specific to GCC, including its statement expressions.

In this case, the block {;} is treated as a (useless) statement expression:

{
  /* nothing */
  ;
  /* nothing */
}

The outermost parentheses ((...)) are there to ensure the parser treats the block as an expression, rather than a more typical empty code block.

compile error when using parenthesis in visual studio but pass in g++/clang++

2 Answers2