C/C++

Snapcraft builds on top of tools like autotools, make, and cmake to create snaps for people to install on Linux.

What problems do snaps solve for C/C++ applications?

Snapcraft bundles necessary libraries required by the application, and can configure the environment for confinement of applications for end user peace of mind. Developers can ensure their application is delivered pre-packaged with libraries which will not be replaced or superceded by a distribution vendor.

Here are some snap advantages that will benefit many C/C++ projects:

  • Simplify installation instructions, regardless of distribution, to snap install myapp.
  • Directly control the delivery of automatic application updates.
  • Bundle all the runtime requirements, including the exact versions of system libraries.
  • Extremely simple creation of services.

How long will this guide take to complete?

Typically this guide will take around 20 minutes and will result in a working C++ application in a snap. Once complete, you’ll understand how to package C/C++ applications as snaps and deliver them to millions of Linux users. After making the snap available in the store, you’ll get access to installation metrics and tools to directly manage the delvery of updates to Linux users.

Getting started

By way of an example, let’s take a look at how a C application can be snapped using snapcraft.

DOSBox Snap

Snaps are defined in a single yaml file placed in the root of your project. The DOSBox example shows the entire snapcraft.yaml for an existing project. We’ll break this down.

name: dosbox
version: "0.74-svn"
summary: DOSBox
description: |
  DOSBox is a x86 emulator with Tandy/Hercules/CGA/EGA/VGA/SVGA graphics
  sound and DOS. It's been designed to run old DOS games under platforms that
  don't support it.

confinement: devmode

apps:
  dosbox:
    command: dosbox

parts:
  dosbox:
    plugin: autotools
    source-type: tar
    source: http://source.dosbox.com/dosboxsvn.tgz
    build-packages:
      - g++
      - make
      - libsdl1.2-dev
      - libpng12-dev
      - libsdl-net1.2-dev
      - libsdl-sound1.2-dev
      - libasound2-dev

Metadata

The snapcraft.yaml starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description or project README.md. This data is used in the presentation of your app in the Snap Store. The summary: can not exceed 79 characters. You can use a pipe in the description: key to declare a multi-line description.

name: dosbox
version: "0.74-svn"
summary: DOSBox
description: |
  DOSBox is a x86 emulator with Tandy/Hercules/CGA/EGA/VGA/SVGA graphics
  sound and DOS. It's been designed to run old DOS games under platforms that
  don't support it.

Confinement

To get started we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the hidden “edge” channel where you and other developers can install them.

confinement: devmode

Parts

Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. In this case we have one: the DOSBox source release tarball. In other cases these can point to local directories, remote git repositories or other revision control systems.

Before building the part the dependencies listed as build-packages are installed. The autotools plugin uses the standard tools, configure and make to build the part.

parts:
  dosbox:
    plugin: autotools
    source-type: tar
    source: http://source.dosbox.com/dosboxsvn.tgz
    build-packages:
      - g++
      - make
      - libsdl1.2-dev
      - libpng12-dev
      - libsdl-net1.2-dev
      - libsdl-sound1.2-dev
      - libasound2-dev

Apps

Apps are the commands and services exposed to end users. If your command name matches the snap name, users will be able run the command directly. If the names differ, then apps are prefixed with the snap name (dosbox.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.

If you don’t want your command prefixed you can request an alias for it on the Snapcraft forum. These are set up automatically when your snap is installed from the Snap Store.

apps:
  dosbox:
    command: dosbox

If your application is intended to run as a service you simply add the line daemon: simple after the command keyword. This will automatically keep the service running on install, update, and reboot.

Building the snap

You’ll first need to install snap support, and then install the snapcraft tool:

sudo snap install --candidate --classic snapcraft

If you have just installed snap support, start a new shell so your PATH is updated to include /snap/bin. You can then build this example yourself:

git clone https://github.com/snapcraft-docs/dosbox
cd dosbox
snapcraft

The resulting snap can be installed locally. This requires the --dangerous flag because the snap is not signed by the Snap Store. The --devmode flag acknowledges that you are installing an unconfined application:

sudo snap install dosbox_*.snap --devmode --dangerous

You can then try it out

dosbox

Removing the snap is simple too:

sudo snap remove dosbox

Share with your friends

To share your snaps you need to publish them in the Snap Store. First, create an account on dashboard.snapcraft.io. Here you can customize how your snaps are presented, review your uploads and control publishing.

You’ll need to choose a unique “developer namespace” as part of the account creation process. This name will be visible by users and associated with your published snaps.

Make sure the snapcraft command is authenticated using the email address attached to your Snap Store account:

snapcraft login

Reserve a name for your snap

You can publish your own version of a snap, provided you do so under a name you have registered.

snapcraft register myapp

Be sure to update the name: in your snapcraft.yaml to match this registered name, then run snapcraft again.

Upload your snap

Use snapcraft to push the snap to the Snap Store.

snapcraft push --release=edge myapp_*.snap

If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.