Does “brew install gcc” installs GNU C++ compiler on macOS

Use brew options. On my machine I get this:

brew options gcc48
--enable-all-languages
        Enable all compilers and languages, except Ada
--enable-cxx
        Build the g++ compiler
--enable-fortran
        Build the gfortran compiler
--enable-java
        Buld the gcj compiler
--enable-multilib
        Build with multilib support
--enable-nls
        Build with native language support (localization)
--enable-objc 
        Enable Objective-C language support
--enable-objcxx
        Enable Objective-C++ language support
--enable-profiled-build
        Make use of profile guided optimization when bootstrapping GCC

Apple stopped shipping gcc with Xcode.

The clang compiler presents itself as gcc (technically I believe it's an llvm front end that respects many gcc flags) when you install Xcode from the Mac App Store:

Mac:~ me$ xcrun --find gcc
/Applications/Xcode.app/Contents/Developer/usr/bin/gcc
Mac:~ me$ `xcrun --find gcc` --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 5.0 (clang-500.2.76) (based on LLVM 3.3svn)
Target: x86_64-apple-darwin12.5.0
Thread model: posix

If you need a different compiler, you'll likely need to download it elsewhere or build it from source.