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Installation: Tools and C++ Runtime

The Cap’n Proto tools, including the compiler (which takes .capnp files and generates source code for them), are written in C++. Therefore, you must install the C++ package even if your actual development language is something else.

This package is licensed under the MIT License.


Cap'n Proto is in BETA

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As of this writing, Cap’n Proto is in beta. The serialization layer is close to feature-complete and we don’t anticipate any further changes to the wire format. That said, if you want to use it, you should keep in mind some caveats:

If you’d like to hack on Cap’n Proto, you should join the discussion group!

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Supported Compilers

Cap’n Proto makes extensive use of C++11 language features. As a result, it requires a relatively new version of a well-supported compiler. The minimum versions are:

If your system’s default compiler is older that the above, you will need to install a newer compiler and set the CXX environment variable before trying to build Cap’n Proto. For example, after installing GCC 4.8, you could set CXX=g++-4.8 to use this compiler.

Supported Operating Systems

In theory, Cap’n Proto should work on any POSIX platform supporting one of the above compilers, as well as on Windows. We test every Cap’n Proto release on the following platforms:

Windows users: As of Visual Studio 2015, Visual C++ still does not support enough of C++11 to compile Cap’n Proto’s reflection or RPC APIs. “Cap’n Proto Lite” omits these features from the library, giving you only the core serialization based on generated code.

Mac OS X users: You must use at least Xcode 5 with the Xcode command-line tools (Xcode menu > Preferences > Downloads). Alternatively, the command-line tools package from Apple or compiler builds from Macports, Fink, or Homebrew are reported to work.

Installation: Unix

From Release Tarball

You may download and install the release version of Cap’n Proto like so:

curl -O https://capnproto.org/capnproto-c++-
tar zxf capnproto-c++-
cd capnproto-c++-
make -j6 check
sudo make install

This will install capnp, the Cap’n Proto command-line tool. It will also install libcapnp, libcapnpc, and libkj in /usr/local/lib and headers in /usr/local/include/capnp and /usr/local/include/kj.

From Package Managers

Some package managers include Cap’n Proto packages.

Note: These packages are not maintained by us and are sometimes not up to date with the latest Cap’n Proto release.

From Git

If you download directly from Git, you will need to have the GNU autotools – autoconf, automake, and libtool – installed. You will also need Subversion installed (in addition to Git) in order to fetch the Google Test sources (done by setup-autotools.sh).

git clone https://github.com/sandstorm-io/capnproto.git
cd capnproto/c++
autoreconf -i
make -j6 check
sudo make install

Installation: Windows

From Release Zip

  1. Download Cap’n Proto Win32 build:

  2. Find capnp.exe, capnpc-c++.exe, and capnpc-capnp.exe under capnproto-tools-win32- in the zip and copy them somewhere.

If you don’t care about C++ support, you can stop here. The compiler exe can be used with plugins provided by projects implementing Cap’n Proto in other languages.

If you want to use Cap’n Proto in C++ with Visual Studio, do the following:

  1. Install CMake version 3.1 or later.

  2. Use CMake to generate Visual Studio project files under capnproto-c++- in the zip file. You will need to enable the CMake project options CAPNP_LITE and EXTERNAL_CAPNP. You can use the CMake UI for this or run this shell command:

    cmake -G "Visual Studio 14 2015" -DCAPNP_LITE=1 -DEXTERNAL_CAPNP=1

    If the capnp.exe and capnpc-c++.exe tools are not on your PATH, then CAPNP_EXECUTABLE and CAPNPC_CXX_EXECUTABLE will need to be set to their respective locations.

  3. Open the “Cap’n Proto” solution in Visual Studio.

  4. Adjust the project build options (e.g., choice of C++ runtime library, enable/disable exceptions and RTTI) to match the options of the project in which you plan to use Cap’n Proto.

  5. Build the solution (ALL_BUILD).

  6. Build the INSTALL project to copy the compiled libraries and header files into CMAKE_INSTALL_PREFIX.

    Alternatively, find the compiled .lib files in the build directory under src/{capnp,kj}/{Debug,Release} and place them somewhere where your project can link against them. Also add the src directory to your search path for #includes, or copy all the headers to your project’s include directory.

  7. Add #define CAPNP_LITE 1 to either your project’s precompiled/shared header or compiler options.

From Git

If you download directly from Git, you’ll need to compile the Cap’n Proto tools (the .exes) using MinGW-w64. This is easiest to do in Cygwin or on Linux. For example, on Debian or Ubuntu, you can install MinGW like so:

sudo apt-get install mingw-w64

You’ll first need to install Cap’n Proto on the host system (using the Unix installation instructions, above). Then, do:

make distclean
./configure --host=i686-w64-mingw32 --with-external-capnp \
  --disable-shared CXXFLAGS='-static-libgcc -static-libstdc++'
make -j6 capnp.exe capnpc-c++.exe capnpc-capnp.exe

Now that you have the exes, you can proceed with the usual Windows compilation instructions.