Why is a stray semicolon no longer detected by `-pedantic` modern compilers?

Why is a stray semicolon no longer detected by `-pedantic` modern compilers?


6

The following snippet generates compilation errors on adding -pedantic and -Werror on compilers that are a bit old.

#include <cstdint>
#include <iostream>

int add(int a, int b){
    return a + b;
}; // <-- stray semicolon

int main (){
    return 0;
}

However this does not happen newer compiler versions. Please find a matrix of gcc (10.x, 11.x) and clang (5.x, 6.x) demonstrating the difference at https://godbolt.org/z/KWeb8WTxz.

I have two parts to my question:

  1. Why is this not triggered in recent compilers?
  2. Is it possible to enable the old behaviour in recent versions of clang or gcc?

Improve this question

2

  • Because it's legal in all declaration contexts now. It wasn't before C++14 (in class scope) even though compiles allowed it.

    – Swift – Friday Pie

    1 hour ago

  • -Wextra-semi catches those.

    – HolyBlackCat

    1 hour ago

1 Answer
1



Reset to default


7

Starting in C++11, extra semicolons ; (aka empty-declarations) at the global level are valid. I believe this is occasionally useful for writing macros.

As such, GCC 11 removed -pedantic diagnostics for an extra ; when -std=c++11 or later is used. See:

You can restore the old behavior by using a C++ standard older than C++11. Both GCC 11 and clang 6 will emit the old diagnostics if you pass -std=c++03.

Improve this answer

2

  • Thank you. My code uses cpp20, so -std=c++03 is not viable. I am getting this on a CentOS compiler where I build python wheels. Any other static-analysis available that you know of that can help? Could you provide an example where this is useful for macros, as mentioned in this answer?

    – jerin

    10 hours ago

  • 3

    @jerin you could have something like an IF_DEBUG macro which removes code outside debug builds. Then, IF_DEBUG(int counter = 0); to declare a debug-only global variable. You could of course put the semicolon inside the macro argument list, but this may mess up auto-formatting with clang-format, and having the semicolon after a function-style macro is preferred by most developers. On a non-debug build, this macro would expand to nothing and you would have an empty-declaration.

    – Jan Schultke

    10 hours ago