Awesome
JlCxx
This is the C++ library component of the CxxWrap.jl package, distributed as a regular CMake library
for use in other C++ projects. To build a Julia interface to a C++ library, you need to build against this library and supply the resulting library as a binary dependency to your Julia package. The testlib-builder
directory contains a complete example of how to build and distribute these binaries, or you can use the BinaryBuilder.jl wizard to generate the builder repository.
See the CxxWrap.jl README for more info on the API.
Building libcxxwrap-julia
Obtaining the source
Simply clone this repository, e.g.:
git clone https://github.com/JuliaInterop/libcxxwrap-julia.git
You can also manage everything directly from Visual Studio Code using "clone git repository" on the start screen.
Preparing the install location
Julia loads the libcxxwrap-julia
through the libcxxwrap_julia_jll package, which is built automatically by BinaryBuilder. To tell Julia to use self-compiled binaries, one way is to use an override
directory. To do this, check out libcxxwrap_julia_jll
for development:
pkg> develop libcxxwrap_julia_jll
Next, import the package and call the dev_jll
function:
julia> import libcxxwrap_julia_jll
julia> libcxxwrap_julia_jll.dev_jll()
Configuring and building
The last command should output the path to the devved JLL, e.g. /home/user/.julia/dev/libcxxwrap_julia_jll
. In that directory, there will be a subdirectory called override
which will contain the binaries from the Julia artifacts distribution. This directory should be completely emptied and then used as build directory from cmake, e.g. in a terminal do:
cd /home/user/.julia/dev/libcxxwrap_julia_jll/override
rm -rf *
cmake -DJulia_PREFIX=/home/user/path/to/julia /path/to/source/of/libcxxwrap-julia
cmake --build . --config Release
Here, /path/to/source/of/libcxxwrap-julia
is the cloned git repository.
Building libcxxwrap-julia requires a C++ compiler which supports C++17 (e.g. GCC 7, clang 5; for macOS users that means Xcode 9.3).
The main CMake option of interest is Julia_PREFIX
, which should point to the Julia installation you want to use. The PREFIX
is a directory, one containing the bin
and lib
directories and so on. If you are using a binary download of Julia (https://julialang.org/downloads/), this is the top-level directory; if you build Julia from source (https://github.com/JuliaLang/julia), it would be the usr
directory of the repository. Below we will call this directory /home/user/path/to/julia
, but you should substitute your actual path in the commands below.
Instead of specifying the prefix, it is also possible to directly set the Julia executable, using:
cmake -DJulia_EXECUTABLE=/home/user/path/to/julia/bin/julia ../libcxxwrap-julia
Next, you can build your own code against this by setting the JlCxx_DIR
CMake variable to the build directory (libcxxwrap-julia-build
) used above, or add it to the CMAKE_PREFIX_PATH
CMake variable.
Using the compiled libcxxwrap-julia in CxxWrap
Following the above instructions, Julia will now automatically use the compiled binaries. You can verify this using:
julia> using CxxWrap
julia> CxxWrap.prefix_path()
"/home/user/.julia/dev/libcxxwrap_julia_jll/override"
An alternative method of using self-compiled binaries is the Overrides.toml
file, to be placed in .julia/artifacts
:
[3eaa8342-bff7-56a5-9981-c04077f7cee7]
libcxxwrap_julia = "/path/to/libcxxwrap-julia-build"
More details here.
The file can be generated automatically using the OVERRIDES_PATH
, OVERRIDE_ROOT
and APPEND_OVERRIDES_TOML
Cmake options, with the caveat that each CMake run will append again to the file and make it invalid, i.e. this is mostly intended for use on CI (see the appveyor and travis files for examples).
Building on Windows
On Windows, building is easiest with Visual Studio 2019, for which the Community Edition with C++ support is a free download. You can clone the https://github.com/JuliaInterop/libcxxwrap-julia.git
repository using the built-in git support, and configure the Julia_PREFIX
option from the built-in CMake support. See the Visual Studio docs for more info.
Binaries for the main branch
Binaries for the main branch are published at https://github.com/barche/libcxxwrap_julia_jll.jl, you can install them (in Pkg mode, hit ]
) using:
add https://github.com/barche/libcxxwrap_julia_jll.jl.git
Using libcxxwrap-julia as a dependency for downstream packages
When developing Julia bindings for a C++ package using libcxxwrap-julia, you need to
build against the correct version of libcxxwrap-julia. Specifically, to make sure that your
wrapper works correctly with
CxxWrap.jl, check the compat
settings for libcxxwrap_jll
in the Project.toml
file of the
latest release of CxxWrap.jl.
It may happen that the latest release of libcxxwrap-julia is not yet supported by
CxxWrap.jl, in which case you should build against an older release (see also
this comment.