Getting Started

To start learning about creating packages, we will create a package from the existing source code repository: https://github.com/memsharded/hello. You can check that project, it is a very simple “hello world” C++ library, using CMake as the build system to build a library and an executable. It does not contain any association with Conan.

We are using a similar GitHub repository as an example, but the same process also applies to other source code origins, like downloading a zip or tarball from the internet.

Note

For this concrete example you will need, besides a C++ compiler, both CMake and git installed and in your path. They are not required by Conan, so you could use your own build system and version control instead.

Creating the Package Recipe

First, let’s create a folder for our package recipe, and use the conan new helper command that will create a working package recipe for us:

$ mkdir mypkg && cd mypkg
$ conan new Hello/0.1 -t

This will generate the following files:

conanfile.py
test_package
  CMakeLists.txt
  conanfile.py
  example.cpp

On the root level, there is a conanfile.py which is the main recipe file, responsible for defining our package. Also, there is a test_package folder, which contains a simple example consuming project that will require and link with the created package. It is useful to make sure that our package is correctly created.

Let’s have a look at the root package recipe conanfile.py:

from conans import ConanFile, CMake, tools

class HelloConan(ConanFile):
    name = "Hello"
    version = "0.1"
    license = "<Put the package license here>"
    url = "<Package recipe repository url here, for issues about the package>"
    description = "<Description of Hello here>"
    settings = "os", "compiler", "build_type", "arch"
    options = {"shared": [True, False]}
    default_options = {"shared": False}
    generators = "cmake"

    def source(self):
        self.run("git clone https://github.com/memsharded/hello.git")
        self.run("cd hello && git checkout static_shared")
        # This small hack might be useful to guarantee proper /MT /MD linkage
        # in MSVC if the packaged project doesn't have variables to set it
        # properly
        tools.replace_in_file("hello/CMakeLists.txt", "PROJECT(MyHello)",
                              '''PROJECT(MyHello)
include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup()''')

    def build(self):
        cmake = CMake(self)
        cmake.configure(source_folder="hello")
        cmake.build()

        # Explicit way:
        # self.run('cmake %s/hello %s'
        #          % (self.source_folder, cmake.command_line))
        # self.run("cmake --build . %s" % cmake.build_config)

    def package(self):
        self.copy("*.h", dst="include", src="hello")
        self.copy("*hello.lib", dst="lib", keep_path=False)
        self.copy("*.dll", dst="bin", keep_path=False)
        self.copy("*.so", dst="lib", keep_path=False)
        self.copy("*.dylib", dst="lib", keep_path=False)
        self.copy("*.a", dst="lib", keep_path=False)

    def package_info(self):
        self.cpp_info.libs = ["hello"]

This is a complete package recipe. Without going into detail, these are the basics:

  • The settings field defines the configuration of the different binary packages. In this example, we defined that any change to the OS, compiler, architecture or build type will generate a different binary package. Please note that Conan generates different binary packages for different introduced configuration (in this case settings) for the same recipe.

    Note that the platform on which the recipe is running and the package being built differ from the final platform where the code will be running (self.settings.os and self.settings.arch) if the package is being cross-built. So if you want to apply a different build depending on the current build machine, you need to check it:

    def build(self):
        if platform.system() == "Windows":
            cmake = CMake(self)
            cmake.configure(source_folder="hello")
            cmake.build()
        else:
            env_build = AutoToolsBuildEnvironment(self)
            env_build.configure()
            env_build.make()
    

    Learn more in the Cross building section.

  • This package recipe is also able to create different binary packages for static and shared libraries with the shared option, which is set by default to False (i.e. by default it will use static linkage).

  • The source() method executes a git clone to retrieve the sources from Github. Other origins, such as downloading a zip file are also available. As you can see, any manipulation of the code can be done, such as checking out any branch or tag, or patching the source code. In this example, we are adding two lines to the existing CMake code, to ensure binary compatibility. Don’t worry about it now, we’ll deal with it later.

  • The build() configures the project, and then proceeds to build it using standard CMake commands. The CMake object just assists to translate the Conan settings to CMake command line arguments. Please note that CMake is not strictly required. You can build packages directly by invoking make, MSBuild, SCons or any other build system.

    See also

    Check the existing build helpers.

  • The package() method copies artifacts (headers, libs) from the build folder to the final package folder.

  • Finally, the package_info() method defines that the consumer must link with the “hello” library when using this package. Other information as include or lib paths can be defined as well. This information is used for files created by generators to be used by consumers, as conanbuildinfo.cmake.

Note

When writing your own conanfile.py references, please bear in mind that you should follow the rules in conanfile.py

The test_package Folder

Note

The test_package differs from the library unit or integration tests, which should be more comprehensive. These tests are “package” tests, and validate that the package is properly created, and that the package consumers will be able to link against it and reuse it.

If you look at the test_package folder, you will realize that the example.cpp and the CMakeLists.txt files don’t have unique characteristics. The test_package/conanfile.py file is just another recipe, that can be perceived as a consumer conanfile.txt that has been displayed in previous sections:

from conans import ConanFile, CMake
import os

class HelloTestConan(ConanFile):
    settings = "os", "compiler", "build_type", "arch"
    generators = "cmake"

    def build(self):
        cmake = CMake(self)
        cmake.configure()
        cmake.build()

    def imports(self):
        self.copy("*.dll", dst="bin", src="bin")
        self.copy("*.dylib*", dst="bin", src="lib")

    def test(self):
        os.chdir("bin")
        self.run(".%sexample" % os.sep)

The conanfile.py described above has the following characteristics:

  • It doesn’t have a name and version, as we are not creating a package so they are not necessary.
  • The package() and package_info() methods are not required since we are not creating a package.
  • The test() method specifies which binaries need to run.
  • The imports() method is set to copy the shared libraries to the bin folder. When dynamic linking is applied, and the test() method launches the example executable, they are found causing the example to run.

Note

An important difference with respect to standard package recipes is that you don’t have to declare a requires attribute to depend on the tested Hello/0.1@demo/testing package as the requires will automatically be injected by Conan during the run. However, if you choose to declare it explicitly, it will work, but you will have to remember to bump the version, and possibly also the user and channel if you decide to change them.

Creating and Testing Packages

You can create and test the package with our default settings simply by running:

$ conan create . demo/testing
...
Hello world!

If “Hello world!” is displayed, it worked.

The conan create command does the following:

  • Copies (“export” in Conan terms) the conanfile.py from the user folder into the local cache.
  • Installs the package, forcing it to be built from the sources.
  • Moves to the test_package folder and creates a temporary build folder.
  • Executes the conan install .., to install the requirements of the test_package/conanfile.py. Note that it will build “Hello” from the sources.
  • Builds and launches the example consuming application, calling the test_package/conanfile.py build() and test() methods respectively.

Using Conan commands, the conan create command would be equivalent to:

$ conan export . demo/testing
$ conan install Hello/0.1@demo/testing --build=Hello
# package is created now, use test to test it
$ conan test test_package Hello/0.1@demo/testing

The conan create command receives the same command line parameters as conan install so you can pass to it the same settings, options, and command line switches. If you want to create and test packages for different configurations, you could:

$ conan create . demo/testing -s build_type=Debug
$ conan create . demo/testing -o Hello:shared=True -s arch=x86
$ conan create . demo/testing -pr my_gcc49_debug_profile
...
$ conan create ...

Settings vs. Options

We have used settings such as os, arch and compiler. Note the above package recipe also contains a shared option (defined as options = {"shared": [True, False]}). What is the difference between settings and options?

Settings are a project-wide configuration, something that typically affects the whole project that is being built. For example, the operating system or the architecture would be naturally the same for all packages in a dependency graph, linking a Linux library for a Windows app, or mixing architectures is impossible.

Settings cannot be defaulted in a package recipe. A recipe for a given library cannot say that its default is os=Windows. The os will be given by the environment in which that recipe is processed. It is a mandatory input.

Settings are configurable. You can edit, add, remove settings or subsettings in your settings.yml file. See the settings.yml reference.

On the other hand, options are a package-specific configuration. Static or shared library are not settings that apply to all packages. Some can be header only libraries while others packages can be just data, or package executables. Packages can contain a mixture of different artifacts. shared is a common option, but packages can define and use any options they want.

Options are defined in the package recipe, including their supported values, while other can be defaulted by the package recipe itself. A package for a library can well define that by default it will be a static library (a typical default). If not specified other. the package will be static.

There are some exceptions to the above. For example, settings can be defined per-package using the command line:

$ conan install . -s MyPkg:compiler=gcc -s compiler=clang ..

This will use gcc for MyPkg and clang for the rest of the dependencies (extremely rare case).

There are situations whereby many packages use the same option, thereby allowing you to set its value once using patterns, like:

$ conan install . -o *:shared=True

Any doubts? Please check out our FAQ section or write us.