VLAs when compiling a C++ source with g++

Question

I understand that VLAs are part of C99 but not C++0x. My question is then why and how g++ would compile code with VLAs. I wrote a test case below:

Answer 1

VLAs are a gcc (and clang) compiler extension in C++ mode, documented here. These extensions are enabled by default.

You should see a warning if you compile with -pedantic.

Funnily, you will not with gcc4.9 and -std=c++14 or -std=c++1y. As they explain here, they removed the -Wvla warning in C++14 mode because VLAs were once in the draft for the standard. They did not actually make it in the final version of C++14.

clang still warns in C++14 mode, as it should.

Edit: gcc 5.1 warns in C++14 mode too, so that got updated correctly.