I just started to get my hands dirty with C/C++, and I am still getting my head around the different concepts (I've written mostly Java previously). I'd really like to know which C/C++ compiler is used and also which standard library is included. Also, I'd like to know where I can find the API documentation of the respective standard library (like the Java SE API docs).
I'm not an XCode user, but it seems to be Apple's LLVM Compiler (by default) according to Apple's website: https://developer.apple.com/technologies/tools/. But, I guess, like any other IDE XCode does support other compilers like GCC. Also depends on your XCode version it seems: http://useyourloaf.com/blog/2011/03/21/compiler-options-in-xcode-gcc-or-llvm.html
Here's a question in SO that asks about the default compiler and the answer seems to have the code to find just that: In Xcode 4.5, what is "Compiler Default" for "C++ Standard Library" and "C++ Language Dialect"?
According to this post 4.6 uses clang instead of GCC for C++: http://cplusplusmusings.wordpress.com/2013/02/26/c-and-xcode-4-6/
P.S.: Googling does help ;)