Skip to content
The Julia C++ Interface
Branch: master
Clone or download
Latest commit 47f5215 Apr 25, 2019
Permalink
Type Name Latest commit message Commit time
Failed to load latest commit information.
deps
docs Upgrade Documenter to 0.20 Apr 25, 2019
src Merge branch 'master' into fix-show Apr 23, 2019
test
.gitignore Bump Julia version and update CI Apr 12, 2019
.travis.yml Bump Julia version and update CI Apr 12, 2019
LICENSE.md
Project.toml `Julia` => `julia` Apr 25, 2019
README.md Update README and warn Windows users Apr 23, 2019
REQUIRE Bump Julia version and update CI Apr 12, 2019
appveyor.yml Enable appveyor and update badge links Apr 12, 2019
codecov.yml Submit coverage and add Travis and Codecov badges to the README Aug 19, 2017

README.md

Cxx.jl

Build Status Build status codecov

The Julia C++ Foreign Function Interface (FFI) and REPL.

REPL Screenshot

Installation

Now, this package provides an out-of-box installation experience on all 64-bit "Tier 1" platforms for Julia 1.1.

pkg> add Cxx

Note that Windows support is still in its early stage, so feel free to submit feedback in the issue tracker.

Build from source

Build requirements

In addition to the system requirements to build julia itself, the following are required:

  • Debian/Ubuntu: libedit-dev, libncurses5-dev
  • RedHat/CentOS: libedit-devel

Building Cxx

Launch Julia (version 1.0 or later), and in the terminal type

pkg> build Cxx

How it works

The main interface provided by Cxx.jl is the @cxx macro. It supports two main usages:

  • Static function call @cxx mynamespace::func(args...)
  • Membercall (where m is a CppPtr, CppRef or CppValue) @cxx m->foo(args...)

To embed C++ functions in Julia, there are two main approaches:

# Using @cxx (e.g.):   
cxx""" void cppfunction(args){ . . .} """ => @cxx cppfunction(args)

# Using icxx (e.g.):
julia_function (args) icxx""" *code here*  """ end

The C++ REPL

This package contains an experimental C++ REPL feature. Using the package will automatically add a new pane to your REPL that is accessible by pressing the < key.

Using Cxx.jl:

Example 1: Embedding a simple C++ function in Julia

# include headers
julia> using Cxx
julia> cxx""" #include<iostream> """  

# Declare the function
julia> cxx"""  
         void mycppfunction() {   
            int z = 0;
            int y = 5;
            int x = 10;
            z = x*y + 2;
            std::cout << "The number is " << z << std::endl;
         }
      """
# Convert C++ to Julia function
julia> julia_function() = @cxx mycppfunction()
julia_function (generic function with 1 method)

# Run the function
julia> julia_function()
The number is 52

Example 2: Pass numeric arguments from Julia to C++

julia> jnum = 10
10

julia> cxx"""
           void printme(int x) {
              std::cout << x << std::endl;
           }
       """

julia> @cxx printme(jnum)
10

Example 3: Pass strings from Julia to C++

julia> cxx"""
         void printme(const char *name) {
            // const char* => std::string
            std::string sname = name;
            // print it out
            std::cout << sname << std::endl;
         }
     """

julia> @cxx printme(pointer("John"))
   John

Example 4: Pass a Julia expression to C++

julia> cxx"""
          void testJuliaPrint() {
              $:(println("\nTo end this test, press any key")::Nothing);
          }
       """

julia> @cxx testJuliaPrint()
       To end this test, press any key

Example 5: Embedding C++ code inside a Julia function

function playing()
    for i = 1:5
        icxx"""
            int tellme;
            std::cout<< "Please enter a number: " << std::endl;
            std::cin >> tellme;
            std::cout<< "\nYour number is "<< tellme << "\n" <<std::endl;
        """
    end
end
playing();

Example 6: Using C++ enums

julia> cxx"""
       class Klassy {
           public:
               enum Foo { Bar, Baz };
               static Foo exec(Foo x) { return x; }
       };
       """
# Access enum
julia> @cxx Klassy::Bar
CppEnum{Symbol("Klassy::Foo")}(0)

# Pass enum as an argument
julia> @cxx Klassy::exec(@cxx(Klassy::Baz))
CppEnum{Symbol("Klassy::Foo")}(1)

Example 7: C++ Hello World class

julia> using Cxx
julia> cxx"""#include <iostream>
       class Hello
       {
           public:
               void hello_world(const char *now){
                   std::string snow = now;
                   std::cout << "Hello World! Now is " << snow << std::endl;
               }
        };"""
julia> hello_class = @cxxnew Hello()
julia> tstamp = string(Dates.now())
julia> @cxx hello_class -> hello_world(pointer(tstamp))
Hello World! Now is 2015-06-19T11:20:31

Example 8: Using C++ with shared libraries

ArrayMaker.h

#ifndef ARRAYMAKER_H
#define ARRAYMAKER_H

class ArrayMaker
{
    private:
        int iNumber;
        float fNumber;
        float* fArr;
    public:
        ArrayMaker(int, float);
        float* fillArr();
};

#endif

ArrayMaker.cpp

#include "ArrayMaker.h"
#include <iostream>

using namespace std;

ArrayMaker::ArrayMaker(int iNum, float fNum) {
    cout << "Got arguments: " << iNum << ", and " << fNum << endl;
    iNumber = iNum;
    fNumber = fNum;
    fArr = new float[iNumber];
}

float* ArrayMaker::fillArr() {
    cout << "Filling the array" << endl;
    for (int i=0; i < iNumber; i++) {
        fArr[i] = fNumber;
        fNumber *= 2;
    }
    return fArr;
}

Compiling into shared library

>> g++ -shared -fPIC ArrayMaker.cpp -o libArrayMaker.so

Using in Julia

julia> using Cxx

# Importing shared library and header file
julia> const path_to_lib = pwd()
julia> addHeaderDir(path_to_lib, kind=C_System)
julia> Libdl.dlopen(path_to_lib * "/libArrayMaker.so", Libdl.RTLD_GLOBAL)
Ptr{Cvoid} @0x000000000728e6d0
julia> cxxinclude("ArrayMaker.h")

# Creating class object
julia> maker = @cxxnew ArrayMaker(5, 2.0)
Got arguments: 5, and 2
Cxx.CppPtr{Cxx.CppValue{Cxx.CppBaseType{:ArrayMaker},(false,false,false)},(false,false,false)}(Ptr{Cvoid} @0x00000000060ab570)

julia> arr = @cxx maker->fillArr()
Filling the array

julia> pointer_to_array(arr, 5)
5-element Array{Float32,1}:
  2.0
  4.0
  8.0
 16.0
 32.0

Troubleshooting

Replacement the current compiler instance

As of now Cxx.jl does not allow redefinition of a function. In order to allow defining the same function multiple times the current compiler instance can be replaced by typing

__current_compiler__ = Cxx.new_clang_instance()
You can’t perform that action at this time.