How can I understand what standard my libraries are and to what standard gcc compiles in my computer?

Question

This is from my terminal:

Korays-MacBook-Pro:~ koraytugay$ gcc --version
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 6.1.0 (clang-602.0.49) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.3.0
Thread model: posix

There are 3 C standards as far as I know, ANSI C, C99 and C11.

How can I know which library I have and what my compiler supports?

Answer 1

You have to find the documentation for your compiler and/or operating system and it's not always clearly documented.

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Apple LLVM version 6.1.0 (clang-602.0.49) (based on LLVM 3.6.0svn)

This corresponds to Xcode 6.3.

https://developer.apple.com/library/mac/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html

Also anything in the LLVM 3.5 release should be in this version of the compiler: the compiler is 'based on the llvm 3.6 svn branch, which exists prior to LLVM.org's 3.6 release (a bit confusing, I know).

http://clang.llvm.org/cxx_status.html

They don't have a similar handy page for C version support, however.

http://llvm.org/releases/3.5.0/tools/clang/docs/UsersManual.html#differences-between-various-standard-modes

In fact it looks to me like the documentation doesn't even accurately reflect clang 3.5's C11 support.

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So basically, if the documentation doesn't clearly cover it, you just have to be familiar with the compiler.

Xcode 6.3 supports C language features for C89/C90, C94, C99, and C11. I believe OS X offers full library support up to C99. OS X does not include an implementation of the C11 standard library, however some C11 headers may be provided by the compiler. <threads.h> isn't, however.

Answer 2

Clang support all three standards and more (“gnu99” from GCC, …). You can find out in the documentation of the commandline option -std which is used to choose them.