# Call c++ library from julia
**URL:** https://discourse.julialang.org/t/call-c-library-from-julia/30653
**Category:** General Usage
**Tags:** cxx
**Created:** [November 3, 2019, 2:39pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653 "2019-11-03T14:39:11Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@bsnyh](https://discourse.julialang.org/u/bsnyh)
#### Post date: [November 3, 2019, 2:39pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/1 "2019-11-03T14:39:11Z")
I need to call a C++ library from Julia. I was thinking to try either Cxx package or CxxWrap package. For Cxx, when I was trying to install this Cxx package to my Julia, get the following error message:
```julia
(v1.1) pkg> add Cxx
Updating registry at `~/.julia/registries/General`
Updating git-repo `https://github.com/JuliaRegistries/General.git`
Resolving package versions...
ERROR: Unsatisfiable requirements detected for package Atom [c52e3926]:
Atom [c52e3926] log:
├─possible versions are: [0.8.0-0.8.8, 0.9.0-0.9.1, 0.10.0-0.10.2, 0.11.0-0.11.3] or uninstalled
└─restricted to versions 0.7.14 by an explicit requirement — no versions left
```
For CxxWrap package, it is not easy for me to understand the boost python hello world example from the github link: [GitHub - JuliaInterop/CxxWrap.jl: Package to make C++ libraries available in Julia](https://github.com/JuliaInterop/CxxWrap.jl)
Could anyone help to provide any references ? Any comments are greatly appreciated.
---
### Author:  [@Elrod](https://discourse.julialang.org/u/Elrod)
#### Post date: [November 3, 2019, 3:17pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/2 "2019-11-03T15:17:53Z")
If you only need a few functions, I’ve found declaring the functions you wish to call `extern "C"` (creating wrappers if necessary), compiling into a shared library, and then `ccall`-ing them to be the simplest approach.
---
### Author:  [@tkoolen](https://discourse.julialang.org/u/tkoolen)
#### Post date: [November 3, 2019, 3:23pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/3 "2019-11-03T15:23:49Z")
To install Cxx, add it to a separate project that doesn’t contain the Juno packages. See also [https://github.com/JunoLab/Juno.jl/issues/265](https://github.com/JunoLab/Juno.jl/issues/265).
---
### Author:  [@bsnyh](https://discourse.julialang.org/u/bsnyh)
#### Post date: [November 3, 2019, 4:15pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/4 "2019-11-03T16:15:47Z")
Thank you for your quick reply. I’m new to Cxx package. I tried to install Cxx in a clean environment, and it did not work either, sigh.
```julia
(v1.0) pkg> activate ~/Desktop/Cxx
[ Info: activating new environment at ~/~/Desktop/Cxx.
(Cxx) pkg> activate
(v1.0) pkg> activate /Desktop/Cxx
[ Info: activating new environment at /Desktop/Cxx.
(Cxx) pkg> add Cxx
Resolving package versions...
ERROR: Unsatisfiable requirements detected for package Cxx [a0b5b9ef]:
Cxx [a0b5b9ef] log:
├─possible versions are: 0.3.0-0.3.2 or uninstalled
├─restricted to versions * by an explicit requirement, leaving only versions 0.3.0-0.3.2
└─restricted by julia compatibility requirements to versions: uninstalled — no versions left
```
I also tried to remove Juno package and install Cxx again, it did not work either.
```julia
julia> Pkg.status()
Status `~/.julia/environments/v1.0/Project.toml`
[c52e3926] Atom v0.9.1
[336ed68f] CSV v0.5.11
[324d7699] CategoricalArrays v0.5.5
[34da2185] Compat v2.1.0
[8f4d0f93] Conda v1.3.0
[1f15a43c] CxxWrap v0.8.2
[a93c6f00] DataFrames v0.19.3
[864edb3b] DataStructures v0.17.0
[31a5f54b] Debugger v0.6.2
[31c24e10] Distributions v0.21.1
[cd3eb016] HTTP v0.8.5
[682c06a0] JSON v0.21.0
[fc18253b] LazyJSON v0.1.1
[522f3ed2] LibExpat v0.5.0
[093fc24a] LightGraphs v1.3.0
[9c8b4983] LightXML v0.8.0
[86cd37e6] OpenStreetMapX v0.1.11 [`~/.julia/dev/OpenStreetMapX`]
[d3d4fdd0] OpenStreetMapXPlot v0.1.2 #master (https://github.com/pszufe/OpenStreetMapXPlot.jl)
[91a5bcdd] Plots v0.26.2
[438e738f] PyCall v1.91.2
[ee283ea6] Rebugger v0.3.2
[189a3867] Reexport v0.2.0
[295af30f] Revise v2.2.0
[90137ffa] StaticArrays v0.11.0
[f3b207a7] StatsPlots v0.10.2
[9a3f8284] Random
(v1.0) pkg> add Cxx
Resolving package versions...
ERROR: Unsatisfiable requirements detected for package Cxx [a0b5b9ef]:
Cxx [a0b5b9ef] log:
├─possible versions are: 0.3.0-0.3.2 or uninstalled
├─restricted to versions * by an explicit requirement, leaving only versions 0.3.0-0.3.2
└─restricted by julia compatibility requirements to versions: uninstalled — no versions left
```
---
### Author:  [@bsnyh](https://discourse.julialang.org/u/bsnyh)
#### Post date: [November 3, 2019, 4:17pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/5 "2019-11-03T16:17:10Z")
Could you provide some examples?
---
### Author:  [@bsnyh](https://discourse.julialang.org/u/bsnyh)
#### Post date: [November 3, 2019, 4:28pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/6 "2019-11-03T16:28:39Z")
I tried julia version 1.2 and it worked. It’s a typical example of “my computer works and I do not know why” 😉
```julia
(v1.2) pkg> add Cxx
Updating registry at `~/.julia/registries/General`
Updating git-repo `https://github.com/JuliaRegistries/General.git`
Resolving package versions...
Installed JuliaFormatter ─ v0.1.19
Installed Cxx ──────────── v0.3.2
Updating `~/.julia/environments/v1.2/Project.toml`
[a0b5b9ef] + Cxx v0.3.2
Updating `~/.julia/environments/v1.2/Manifest.toml`
[b99e7846] ↑ BinaryProvider v0.5.6 ⇒ v0.5.7
[a0b5b9ef] + Cxx v0.3.2
[1a297f60] ↑ FillArrays v0.7.3 ⇒ v0.7.4
[f6369f11] ↑ ForwardDiff v0.10.3 ⇒ v0.10.5
[28b8d3ca] ↑ GR v0.41.0 ⇒ v0.42.0
[eafb193a] ↑ Highlights v0.4.4 ⇒ v0.4.5
[a98d9a8b] ↑ Interpolations v0.12.2 ⇒ v0.12.4
[98e50ef6] ↑ JuliaFormatter v0.1.16 ⇒ v0.1.19
[429524aa] ↑ Optim v0.19.3 ⇒ v0.19.4
[85a6dd25] ↑ PositiveFactorizations v0.2.2 ⇒ v0.2.3
Building Cxx → `~/.julia/packages/Cxx/vxYtJ/deps/build.log`
```
---
### Author:  [@bsnyh](https://discourse.julialang.org/u/bsnyh)
#### Post date: [November 3, 2019, 5:16pm UTC](https://discourse.julialang.org/t/call-c-library-from-julia/30653/7 "2019-11-03T17:16:44Z")
I’ve already got some examples to use shared library and Cxx package.