How to enforce C89-style variable declarations in gcc?

Question

I work on a code base which is mostly C with a little C++, and is mostly built with gcc but occasionally it needs to be built with MSVC. Microsoft\'s C compiler is still pretty

Answer 1

You're after the -Wall -Wextra -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations and -Wdeclaration-after-statement options, as described on the gcc warnings info page. Note that these can cause a lot of noise from issues in system header files, and they're only warnings so you've got to have a policy of being keen to have a zero-warning build.