Getting started

As an example, let’s start with one of the most popular C++ libraries: POCO. Conan works with any build system and it does not depend on CMake, though we will use CMake for this example for convenience.

A Timer using POCO libraries

First, let’s create a folder for our project:

$ mkdir mytimer
$ cd mytimer

Note

If you have the code in a github repository, instead of creating the folder, you can just clone the project:

$ git clone https://github.com/memsharded/example-poco-timer.git mytimer

Create the following source files inside that folder:

timer.cpp
 // $Id: //poco/1.4/Foundation/samples/Timer/src/Timer.cpp#1 $
 // This sample demonstrates the Timer and Stopwatch classes.
 // Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
 // and Contributors.
 // SPDX-License-Identifier:    BSL-1.0

 #include "Poco/Timer.h"
 #include "Poco/Thread.h"
 #include "Poco/Stopwatch.h"
 #include <iostream>

 using Poco::Timer;
 using Poco::TimerCallback;
 using Poco::Thread;
 using Poco::Stopwatch;

 class TimerExample{
 public:
     TimerExample(){ _sw.start();}

     void onTimer(Timer& timer){
         std::cout << "Callback called after " << _sw.elapsed()/1000 << " milliseconds." << std::endl;
     }
 private:
     Stopwatch _sw;
 };

 int main(int argc, char** argv){
     TimerExample example;
     Timer timer(250, 500);
     timer.start(TimerCallback<TimerExample>(example, &TimerExample::onTimer));

     Thread::sleep(5000);
     timer.stop();
     return 0;
 }

Now, also create a conanfile.txt inside the same folder with the following content:

conanfile.txt
 [requires]
 Poco/1.8.0.1@pocoproject/stable

 [generators]
 cmake

In this example we will use CMake to build the project, which is why the cmake generator is specified. This generator will create a conanbuildinfo.cmake file that defines CMake variables as include paths and library names, that can be used in our build.

Note

If you are not a CMake user, change the [generators] section of your conanfile.txt to gcc or a more generic one txt to handle requirements with any build system. Learn more in Using packages.

Just include the generated file and use those variables inside our own CMakeLists.txt:

CMakeLists.txt
 project(FoundationTimer)
 cmake_minimum_required(VERSION 2.8.12)
 add_definitions("-std=c++11")

 include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
 conan_basic_setup()

 add_executable(timer timer.cpp)
 target_link_libraries(timer ${CONAN_LIBS})

Installing dependencies

If you have a terminal with light colors, like the default gnome terminal in Ubuntu, set CONAN_COLOR_DARK=1 to have a better contrast. Then create a build folder, so temporary build files are put there, and install the requirements (pointing to the parent directory, as it is where the conanfile.txt is):

$ mkdir build && cd build
$ conan install ..

This install command will download the binary package required for your configuration (detected the first time that you ran the conan command), together with other (transitively required by Poco) libraries, like OpenSSL and Zlib. It will also create the conanbuildinfo.cmake file in the current directory, in which you can see the cmake defined variables, and a conaninfo.txt where information about settings, requirements and options is saved.

It is very important to understand the installation process. When a conan install command is issued, it will use some settings, specified on the command line or taken from the defaults in <userhome>/.conan/profiles/default file.

_images/install_flow.png

So for a command like $ conan install -s os="Linux" -s compiler="gcc", the steps are:

  • First check if the package recipe (for Poco/1.8.0.1@pocoproject/stable package) exists in the local cache. If we are just starting, our cache will be empty.
  • Look for the package recipe in the defined remotes. By default, conan comes with the Bintray remotes defined (you can change that), so the conan client will search in conan-center and conan-transit for the recipe.
  • If the recipe exists, conan client will fetch and store it in your local cache.
  • With the package recipe and the input settings (Linux, gcc), conan client will check in the local cache if the corresponding binary is there, if we are installing for the first time, it won’t.
  • Conan client will search for the corresponding binary package in the remote, if it exists, it will be fetched.
  • Conan client will then finish generating the requested files specified in generators.

If the binary package necessary for some given settings doesn’t exist, conan client will throw an error. It is possible to try to build the binary package from sources with the --build missing command line argument to install. Detailed explanations about how a binary package is built from sources will be given in a later section.

Warning

In the Bintray repositories there are binaries for several mainstream compilers and versions, like Visual Studio 12, 14, linux-gcc 4.9 and apple-clang 3.5. If you are using another setup, the command might fail because of the missing package. You could try to change your settings or build the package from source, using the --build missing option, instead of retrieving the binaries. Such a build might not have been tested and eventually fail.

Building the timer example

Now, you are ready to build and run your project:

(win)
$ cmake .. -G "Visual Studio 14 Win64"
$ cmake --build . --config Release

(linux, mac)
$ cmake .. -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
$ cmake --build .
...
[100%] Built target timer
$ ./bin/timer
Callback called after 250 milliseconds.
...

Inspecting dependencies

The retrieved packages have been installed to your local user cache (typically .conan/data), so they can be reused from there in other projects, and allow to clean your current project and keep working even without network connection. To search packages in the local cache you can do:

$ conan search

You can also inspect the binary packages (for different installed binaries for a given package recipe) details with:

$ conan search Poco/1.8.0.1@pocoproject/stable

You can also generate a table for all binaries from a given recipe with the --table option, even in remotes:

$ conan search zlib/1.2.11@conan/stable --table=file.html -r=conan-center
$ file.html # or open the file, double-click
_images/search_binary_table.png

Please check the reference for more information on how to search in remotes, or how to remove or clean packages from the local cache, or how to define custom cache directory per user or per project.

You can also inspect your current project’s dependencies with the info command, pointing it to the folder where the conanfile.txt is:

$ conan info ..

You can generate a graph of your dependencies, in dot or html formats:

$ conan info .. --graph=file.html
$ file.html # or open the file, double-click
_images/info_deps_html_graph.png

Building with other configurations

In this example we have built our project using the default configuration detected by conan, this configuration is known as the default profile.

The first time you run the conan command, your settings are detected (compiler, architecture…) automatically and stored as default in a profile. You can change your those settings by editing ~/.conan/profiles/default or create new profiles with the desired configuration.

For example, if we have a profile with a gcc configutarion for 32 bits in a profile called gcc_x86, we could issue the install command like this:

$ conan install . -pr gcc_x86

Tip

Using profiles is strongly recommended. Learn more about them here.

However, the user can always override the default profile settings in install command with the -s parameter. As an exercise to the reader, let’s try building the timer project with a different configuration. For example, building the 32 bits version:

$ conan install . -s arch=x86

This will install a different package, using the -s arch=x86 setting, instead of the default used previously, that in most cases will be x86_64.

To use the 32 bits binaries you will also have to change your project build:
  • In Windows, change the CMake invocation accordingly to Visual Studio 14.
  • In Linux, you have to add the -m32 flag to your CMakeLists.txt with SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -m32"), and the same to CMAKE_C_FLAGS, CMAKE_SHARED_LINK_FLAGS and CMAKE_EXE_LINKER_FLAGS. This can also be done more easily, automatically with conan, as we’ll see later.
  • In Mac, you need to add the definition -DCMAKE_OSX_ARCHITECTURES=i386.

Got any doubts? Please check out our FAQ section or write to us.