如何确保我的默认 C/C++ 编译器是 GCC

Question

I'm trying to install Riak from source on macOS ( https://docs.riak.com/riak/kv/2.2.3/setup/installing/mac-osx.1.html#installing-from-source ).

There is a note:

Riak will not compile with Clang. Please make sure that your default C/C++ compiler is GCC

How do I find out which compiler is the default and how to change it?

macOS Catalina (10.15.4), which command prints:

$ which clang
/usr/bin/clang
$ which gcc
/usr/bin/gcc

Answer 1

On macOS Catalina (and prior versions, and most likely subsequent versions too), there are two aspects to the problem and some suggested solutions.

What is the name of the compiler used by make by default?

$ mkdir junk
$ cd junk
$ > x.cpp
$ > y.c
$ make x y
c++     x.cpp   -o x
cc     y.c   -o y
$ cd ..
$ rm -fr junk

This shows that the names used by make are cc and c++ . Those are not obviously clang or clang++ , but neither are they obviously gcc and g++ .

$ which cc c++
/usr/bin/cc
/usr/bin/c++
$

Which compiler is it really?

Which compiler really lives behind the names cc , c++ , gcc , g++ , clang , and clang++ ? We can check which compiler these really are by getting them to identify their version:

$ for compiler in cc c++ gcc g++ clang clang++
> do
>     which $compiler
>     $compiler --version
> done
/usr/bin/cc
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/c++
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/gcc
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/g++
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/clang
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
/usr/bin/clang++
Apple clang version 11.0.0 (clang-1100.0.33.17)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$

As you can see, the versions installed in /usr/bin are all the same compiler, and that compiler is clang or clang++ .

This was run on a machine with macOS Mojave 10.14.6 and XCode 11.3.1. The latest version of XCode — 11.4.1 — is only available on Catalina. However, the general conclusion is the same — all the C and C++ compilers are really clang and clang++ in disguise.

How do you get GNU GCC onto your machine?

How do you get a real GNU GCC — a real GCC, not clang in disguise — onto your machine?

• Use Brew to install GCC (I've not checked which version of GCC is current).
• Or use MacPorts (again, I've not checked which version of GCC is current).
• If you're adventuresome, do it yourself (but I've not yet succeeded at building GCC 9.3.0 on Catalina; I have a GCC 9.2.0 built on macOS Mojave 10.14.x that works OK on Catalina though — with one environment variable needed to locate the headers).
• Maybe Fink — it lists GCC 8.4 as being made available in 2020; I don't know about newer versions.

Be aware that Apple has taken to hiding the system header files miles out of the way (not in /usr/include — and you can't modify that part of the file system to add a symlink to where they've hidden them):

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include

(You mean you couldn't guess that? Me neither!)

How do you change the default compiler?

Once you have GCC installed somewhere appropriate, you need to ensure you use the 'real' GCC and not the 'fake' in /usr/bin . You do that in part by ensuring that the bin directory for the 'real' GCC occurs on your PATH before /usr/bin . I have GCC 9.3.0 installed under /opt/gcc/v9.3.0 , so /opt/gcc/v9.3.0/bin appears on my PATH long before /usr/bin does.

You also need to ensure that the configuration for riak (the software you're installing) uses the correct compilers. If there's a ./configure script, run it with the correct path specified for the compilers. For example, I might use:

./configure CC=/opt/gcc/v9.3.0/bin/gcc CXX=/opt/gcc/v9.3.0/bin/g++

You can also set these values as environment variables.

If it uses cmake or some other configuration package, you'll need to consult the installation instructions. That's usually README or sometimes INSTALL .

---

See also (increasingly older posts):

• Can't compile a C program on a Mac after upgrade to Catalina
• Can't compile a C program on a Mac after upgrade to Mojave
• Install GNU GCC on a Mac