How run clang from command line on Windows?

Question

At the Going Native conference last week, Chandler Carruth announced the existence of prebuilt binaries for running clang on windows. The same information is in a blog post here. The intended audience for this is users of Visual Studio, but I want to run clang from the command line.

I ran the installer and added the LLVM bin directory to my path, but when I try to compile "Hello world", I get this:

C:\>clang hello.cpp hello.cpp:1:10: fatal error: 'iostream' file not found #include <iostream>          ^ 1 error generated. 

I can't find any information on how to configure things to run clang on Windows, and I'm guessing that after I figure out how to tell clang where to search for standard library headers, I'll have to tell it where to look for libraries to link with. Can somebody walk me through the setup step by step or point me to such a walkthrough?

Answer 1

This is a old question, and a lot has changed since then. Given this is a common problem when trying Clang on Windows, it deserves an updated answer.

As of 2017, with the LLVM 3.9.1 build for Windows, you need the following to be able to invoke clang from your shell.

VC++ Build Tools

We still do not have a libc++ port for Windows, so Clang uses the VC++ libraries as well as the VC++ linker.

So first of all you need the VC++ Build Tools on your system. Do note you already have those installed if you happen to have the Visual C++ IDE.

Environment Variables

You need to tell Clang where to find the build tools and its libraries.

Option 1 (vcvarsall.bat)

This is the easiest and standard option.

Run

> "%VS140COMNTOOLS%../../VC/vcvarsall.bat" amd64

Replacing amd64 with your target architecture on Clang, which may be x86, amd64 or arm. You may replace %VS140COMNTOOLS% as well if you have a different version of the VC++ toolset.

As a shortcut, you could run the Visual C++ Command Prompt instead of cmd+vcvarsall, since you need to call this batch for every command prompt you open.

Now you are able to enjoy Clang.

Option 2 (Manually)

In case you cannot run vcvarsall.bat or want to automate this process, welcome, I had the same need.

All of the following environments variables are set automatically by vcvarsall.bat, so you can run that and take your machine values from there. I'll give mines as examples and in the hope it's the same elsewhere.

Set the INCLUDE environment variable to C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE;C:\Program Files (x86)\Windows Kits\10\include\10.0.10240.0\ucrt;C:\Program Files (x86)\Windows Kits\8.1\include\shared;C:\Program Files (x86)\Windows Kits\8.1\include\um;C:\Program Files (x86)\Windows Kits\8.1\include\winrt;

Set LIB to C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\LIB\amd64;C:\Program Files (x86)\Windows Kits\10\lib\10.0.10240.0\ucrt\x64;C:\Program Files (x86)\Windows Kits\8.1\lib\winv6.3\um\x64;. Do note the architecture specific components!

For the build tools, you can either have the tools on PATH or setup the VCINSTALLDIR environment variable. Clang will try both, favoring VCINSTALLDIR.

Set VCINSTALLDIR to %VS140COMNTOOLS%../../VC or add %VS140COMNTOOLS%../../VC/bin/amd64 to your PATH.

Footnote

This is all very under documented, so the requirements may change at any time, but the Clang MSVC driver is trying to automate this as much as possible, by querying the Windows Register and many other tricks, so none of this may be necessary anymore in the future.