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---
layout: documentation
title: Windows
---
# Using Bazel on Windows
## <a name="install"></a>Installation
See [Install Bazel on Windows](install-windows.html) for installation
instructions.
## Known issues
We mark Windows-related Bazel issues on GitHub with the "platform:windows"
label. [You can see the open issues here.](https://github.com/bazelbuild/bazel/issues?q=is%3Aopen+is%3Aissue+label%3A%22platform%3A+windows%22)
## Running Bazel: MSYS2 shell vs. Command Prompt vs. PowerShell
It's best to run Bazel from the Command Prompt (`cmd.exe`) or from PowerShell.
You can also run Bazel from the MSYS2 shell, but you need to disable MSYS2's
automatic path conversion. See [this StackOverflow
answer](https://stackoverflow.com/a/49004265/7778502) for details.
## Setting environment variables
Environment variables you set in the Windows Command Prompt (`cmd.exe`) are only
set in that command prompt session. If you start a new `cmd.exe`, you need to
set the variables again. To always set the variables when `cmd.exe` starts, you
can add them to the User variables or System variables in the `Control Panel >
System Properties > Advanced > Environment Variables...` dialog box.
## <a name="using"></a>Using Bazel on Windows
The first time you build any target, Bazel auto-configures the location of
Python and the Visual C++ compiler. If you need to auto-configure again, run
`bazel clean` then build a target.
You can also tell Bazel where to find the Python binary and the C++ compiler:
- use the [`--python_path=c:\path\to\python.exe`](command-line-reference.html#flag--python_path) flag for Python
- use the `BAZEL_VC` or the `BAZEL_VS` environment variable (they are *not* the same!).
See the [Build C++ section](#build_cpp) below.
### <a name="build_cpp"></a>Build C++
To build C++ targets, you need:
* The Visual C++ compiler.
You can install it in one of the following ways:
* Install [Visual Studio 2015 or later](https://www.visualstudio.com/)
(Community Edition is enough) with Visual C++.
Make sure to also install the `Visual C++ > Common Tools for Visual C++`
and `Visual C++ > Microsoft Foundation Classes for C++` features. These
features are not installed by default.
* Install the [Visual C++ Build
Tools 2015 or later](https://visualstudio.microsoft.com/downloads/#build-tools-for-visual-studio-2017).
If [alwayslink](be/c-cpp.html#cc_library.alwayslink) doesn't work with
VS 2017, that is due to a
[known issue](https://github.com/bazelbuild/bazel/issues/3949),
please upgrade your VS 2017 to the latest version.
* The `BAZEL_VS` or `BAZEL_VC` environment variable. (They are *not* the same!)
Bazel tries to locate the C++ compiler the first time you build any
target. To tell Bazel where the compiler is, you can set one of the
following environment variables:
* `BAZEL_VS` storing the Visual Studio installation directory
* `BAZEL_VC` storing the Visual C++ Build Tools installation directory
Setting one of these variables is enough. For example:
```
set BAZEL_VS=C:\Program Files (x86)\Microsoft Visual Studio 14.0
```
or
```
set BAZEL_VC=C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC
```
The first command sets the path to Visual Studio (BAZEL\_V<b>S</b>), the other
sets the path to Visual C++ (BAZEL\_V<b>C</b>).
* The [Windows
SDK](https://developer.microsoft.com/en-us/windows/downloads/windows-10-sdk).
The Windows SDK contains header files and libraries you need when building
Windows applications, including Bazel itself.
If everything is set up, you can build a C++ target now!
Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):
```
C:\projects\bazel> bazel build //examples/cpp:hello-world
C:\projects\bazel> bazel-bin\examples\cpp\hello-world.exe
```
### Build Java
There's no setup necessary.
On Windows, Bazel builds two output files for `java_binary` rules:
* a `.jar` file
* a `.exe` file that can set up the environment for the JVM and run the binary
Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):
```
C:\projects\bazel> bazel build //examples/java-native/src/main/java/com/example/myproject:hello-world
C:\projects\bazel> bazel-bin\examples\java-native\src\main\java\com\example\myproject\hello-world.exe
```
### Build Python
To build Python targets, you need:
* The [Python interpreter](https://www.python.org/downloads/)
Both Python 2 and Python 3 are supported.
To tell Bazel where Python is, you can use `--python_path=<path/to/python>`.
For example:
```
bazel build --python_path=C:/Python27/python.exe ...
```
If `--python_path` is not specified, Bazel uses `python.exe` as
the interpreter and the binary looks for it in `$PATH` during runtime.
If it is not in `$PATH`(for example, when you use `py_binary` as an action's
executable, Bazel will sanitize `$PATH`), then the execution will fail.
On Windows, Bazel builds two output files for `py_binary` rules:
* a self-extracting zip file
* an executable file that can launch the Python interpreter with the
self-extracting zip file as the argument
You can either run the executable file (it has a `.exe` extension) or you can run
Python with the self-extracting zip file as the argument.
Try building a target from one of our [sample
projects](https://github.com/bazelbuild/bazel/tree/master/examples):
```
C:\projects\bazel> bazel build //examples/py_native:bin
C:\projects\bazel> bazel-bin\examples\py_native\bin.exe
C:\projects\bazel> python bazel-bin\examples\py_native\bin.zip
```
If you are interested in details about how Bazel builds Python targets on
Windows, check out this [design
doc](https://bazel.build/designs/2016/09/05/build-python-on-windows.html).
|
