Getting Started

Let’s get started with an example: We are going to create an MD5 hash calculator app that uses one of the most popular C++ libraries: Poco.

We’ll use CMake as build system in this case but keep in mind that Conan works with any build system and is not limited to using CMake.

Make sure you are running the latest Conan version. Read the Conan update section to get more information.

An MD5 hash calculator using the Poco Libraries

Note

The source files to recreate this project are available in the example repository in GitHub. You can skip the manual creation of the folder and sources with this command:

$ git clone https://github.com/conan-io/examples.git && cd examples/libraries/poco/md5
  1. Create the following source file inside a folder. This will be the source file of our application:

    md5.cpp
     #include "Poco/MD5Engine.h"
     #include "Poco/DigestStream.h"
    
     #include <iostream>
    
     int main(int argc, char** argv){
         Poco::MD5Engine md5;
         Poco::DigestOutputStream ds(md5);
         ds << "abcdefghijklmnopqrstuvwxyz";
         ds.close();
         std::cout << Poco::DigestEngine::digestToHex(md5.digest()) << std::endl;
         return 0;
     }
    
  2. We know that our application relies on the Poco libraries. Let’s look for it in the ConanCenter remote, going to https://conan.io/center, and typing “poco” in the search box. We will see that there are some different versions available:

    poco/1.8.1
    poco/1.9.3
    poco/1.9.4
    ...
    

    Note

    The Conan client contains a command to search in remote repositories, and we could try $ conan search poco --remote=conan-center. You can perfectly use this command to search in your own repositories, but note that at the moment this might timeout in ConanCenter. The infrastructure is being improved to support this command too, but meanwhile using the ConanCenter UI is recommended.

  3. We got some interesting references for Poco. Let’s inspect the metadata of the 1.9.4 version:

    $ conan inspect poco/1.9.4
    name: poco
    version: 1.9.4
    url: https://github.com/conan-io/conan-center-index
    homepage: https://pocoproject.org
    license: BSL-1.0
    author: None
    description: Modern, powerful open source C++ class libraries for building network- and internet-based applications that run on desktop, server, mobile and embedded systems.
    topics: ('conan', 'poco', 'building', 'networking', 'server', 'mobile', 'embedded')
    generators: cmake
    exports: None
    exports_sources: CMakeLists.txt
    short_paths: False
    apply_env: True
    build_policy: None
    revision_mode: hash
    settings: ('os', 'arch', 'compiler', 'build_type')
    options:
        cxx_14: [True, False]
        enable_apacheconnector: [True, False]
        enable_cppparser: [True, False]
        enable_crypto: [True, False]
        [...]
    default_options:
        cxx_14: False
        enable_apacheconnector: False
        enable_cppparser: False
        enable_crypto: True
        [...]
    
  4. Let’s use this poco/1.9.4 version for our MD5 calculator app, creating a conanfile.txt inside our project’s folder with the following content:

    conanfile.txt
     [requires]
     poco/1.9.4
    
     [generators]
     cmake
    

    In this example we are using CMake to build the project, which is why the cmake generator is specified. This generator creates a conanbuildinfo.cmake file that defines CMake variables including paths and library names that can be used in our build. Read more about Generators.

  5. Next step: We are going to install the required dependencies and generate the information for the build system:

    Important

    If you are using GCC compiler >= 5.1, Conan will set the compiler.libcxx to the old ABI for backwards compatibility. In the context of this getting started example, this is a bad choice though: Recent gcc versions will compile the example by default with the new ABI and linking will fail without further customization of your cmake configuration. You can avoid this with the following commands:

    $ conan profile new default --detect  # Generates default profile detecting GCC and sets old ABI
    $ conan profile update settings.compiler.libcxx=libstdc++11 default  # Sets libcxx to C++11 ABI
    

    You will find more information in How to manage the GCC >= 5 ABI.

    $ mkdir build && cd build
    $ conan install ..
    ...
    Requirements
        bzip2/1.0.8 from 'conan-center' - Downloaded
        expat/2.2.9 from 'conan-center' - Downloaded
        openssl/1.1.1g from 'conan-center' - Downloaded
        pcre/8.41 from 'conan-center' - Downloaded
        poco/1.9.4 from 'conan-center' - Cache
        sqlite3/3.31.1 from 'conan-center' - Downloaded
        zlib/1.2.11 from 'conan-center' - Downloaded
    Packages
        bzip2/1.0.8:5be2b7a2110ec8acdbf9a1cea9de5d60747edb34 - Download
        expat/2.2.9:6cc50b139b9c3d27b3e9042d5f5372d327b3a9f7 - Download
        openssl/1.1.1g:6cc50b139b9c3d27b3e9042d5f5372d327b3a9f7 - Download
        pcre/8.41:20fc3dfce989c458ac2372442673140ea8028c06 - Download
        poco/1.9.4:73e83a21ea6817fa9ef0f7d1a86ea923190b0205 - Download
        sqlite3/3.31.1:4559c5d4f09161e1edf374b033b1d6464826db16 - Download
        zlib/1.2.11:6cc50b139b9c3d27b3e9042d5f5372d327b3a9f7 - Download
    
    zlib/1.2.11: Retrieving package f74366f76f700cc6e991285892ad7a23c30e6d47 from remote 'conan-center'
    Downloading conanmanifest.txt completed [0.25k]
    Downloading conaninfo.txt completed [0.44k]
    Downloading conan_package.tgz completed [83.15k]
    Decompressing conan_package.tgz completed [0.00k]
    zlib/1.2.11: Package installed f74366f76f700cc6e991285892ad7a23c30e6d47
    zlib/1.2.11: Downloaded package revision 0
    ...
    poco/1.9.4: Retrieving package 645aaff0a79e6036c77803601e44677556109dd9 from remote 'conan-center'
    Downloading conanmanifest.txt completed [48.75k]
    Downloading conaninfo.txt completed [2.44k]
    Downloading conan_package.tgz completed [5128.39k]
    Decompressing conan_package.tgz completed [0.00k]
    poco/1.9.4: Package installed 645aaff0a79e6036c77803601e44677556109dd9
    poco/1.9.4: Downloaded package revision 0
    conanfile.txt: Generator cmake created conanbuildinfo.cmake
    conanfile.txt: Generator txt created conanbuildinfo.txt
    conanfile.txt: Generated conaninfo.txt
    conanfile.txt: Generated graphinfo
    

    Conan installed our Poco dependency but also the transitive dependencies for it: OpenSSL, zlib, sqlite and others. It has also generated a conanbuildinfo.cmake file for our build system.

    Warning

    There are prebuilt binaries for several mainstream compilers and versions available in Conan Center repository, such as Visual Studio 14, 15, Linux GCC 4.9 and Apple Clang 3.5. Up to >130 different binaries for different configurations can be available in ConanCenter. But if your current configuration is not pre-built in ConanCenter, Conan will raise a “BinaryMissing” error. Please read carefully the error messages. You can build the binary package from sources using conan install .. --build=missing, it will succeed if your configuration is supported by the recipe (it is possible that some ConanCenter recipes fail to build for some platforms). You will find more info in the Building with other configurations section.

  6. Now let’s create our build file. To inject the Conan information, include the generated conanbuildinfo.cmake file like this:

    CMakeLists.txt
     cmake_minimum_required(VERSION 2.8.12)
     project(MD5Encrypter)
    
     add_definitions("-std=c++11")
    
     include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
     conan_basic_setup()
    
     add_executable(md5 md5.cpp)
     target_link_libraries(md5 ${CONAN_LIBS})
    

    Note

    There are other integrations with CMake, like the cmake_find_package generators, that will use the find_package() CMake syntax (see CMake section).

  7. Now we are ready to build and run our MD5 app:

    (win)
    $ cmake .. -G "Visual Studio 16"
    $ cmake --build . --config Release
    
    (linux, mac)
    $ cmake .. -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
    $ cmake --build .
    ...
    [100%] Built target md5
    $ ./bin/md5
    c3fcd3d76192e4007dfb496cca67e13b
    

Installing Dependencies

The conan install command downloads the binary package required for your configuration (detected the first time you ran the 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 variables, and a conaninfo.txt in which the settings, requirements and optional information is saved.

Note

Conan generates a default profile with your detected settings (OS, compiler, architecture…) and that configuration is printed at the top of every conan install command. However, it is strongly recommended to review it and adjust the settings to accurately describe your system as shown in the Building with other configurations section.

It is very important to understand the installation process. When the conan install command runs, settings specified on the command line or taken from the defaults in <userhome>/.conan/profiles/default file are applied.

_images/conan-install_flow.png

For example, the command conan install .. --settings os="Linux" --settings compiler="gcc", performs these steps:

  • Checks if the package recipe (for poco/1.9.4 package) exists in the local cache. If we are just starting, the cache is empty.
  • Looks for the package recipe in the defined remotes. Conan comes with conan-center remote as the default, but can be changed.
  • If the recipe exists, the Conan client fetches and stores it in your local Conan cache.
  • With the package recipe and the input settings (Linux, GCC), Conan looks for the corresponding binary in the local cache.
  • As the binary is not found in the cache, Conan looks for it in the remote and fetches it.
  • Finally, it generates an appropriate file for the build system specified in the [generators] section.

Inspecting Dependencies

The retrieved packages are installed to your local user cache (typically .conan/data), and can be reused from this location for other projects. This allows to clean your current project and continue working even without network connection. To search for packages in the local cache run:

$ conan search "*"
Existing package recipes:

openssl/1.0.2t
poco/1.9.4
zlib/1.2.11
...

To inspect the different binary packages of a reference run:

$ conan search poco/1.9.4@
Existing packages for recipe poco/1.9.4:

Package_ID: 645aaff0a79e6036c77803601e44677556109dd9
    [options]
        cxx_14: False
        enable_apacheconnector: False
        enable_cppparser: False
        enable_crypto: True
        enable_data: True
...

The @ symbol at the end of the package name is important to search for a specific package. If you don’t add the @, Conan will interpret the argument as a pattern search and return all the packages that match the poco/1.9.4 pattern and may have different user and channel.

To inspect all your current project’s dependencies use the conan info command by pointing it to the location of the conanfile.txt folder:

$ conan info ..
conanfile.txt
    ID: db91af4811b080e02ebe5a626f1d256bb90d5223
    BuildID: None
    Requires:
        poco/1.9.4
openssl/1.0.2t
    ID: eb50d18a5a5d59bd0c332464a4c348ab65e353bf
    BuildID: None
    Remote: conan-center=https://center.conan.io
    URL: https://github.com/conan-io/conan-center-index
    Homepage: https://github.com/openssl/openssl
    License: OpenSSL
    Description: A toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols
    Topics: conan, openssl, ssl, tls, encryption, security
    Recipe: Cache
    Binary: Cache
    Binary remote: conan-center
    Creation date: 2019-11-13 23:14:37
    Required by:
        poco/1.9.4
    Requires:
        zlib/1.2.11
poco/1.9.4
    ID: 645aaff0a79e6036c77803601e44677556109dd9
    BuildID: None
    Remote: conan-center=https://center.conan.io
    URL: https://github.com/conan-io/conan-center-index
    Homepage: https://pocoproject.org
    License: BSL-1.0
    Description: Modern, powerful open source C++ class libraries for building network- and internet-based applications that run on desktop, server, mobile and embedded systems.
    Topics: conan, poco, building, networking, server, mobile, embedded
    Recipe: Cache
    Binary: Cache
    Binary remote: conan-center
    Creation date: 2020-01-07 17:29:24
    Required by:
        conanfile.txt
    Requires:
        openssl/1.0.2t
zlib/1.2.11
    ID: f74366f76f700cc6e991285892ad7a23c30e6d47
    BuildID: None
    Remote: conan-center=https://center.conan.io
    URL: https://github.com/conan-io/conan-center-index
    Homepage: https://zlib.net
    License: Zlib
    Description: A Massively Spiffy Yet Delicately Unobtrusive Compression Library (Also Free, Not to Mention Unencumbered by Patents)
    Recipe: Cache
    Binary: Cache
    Binary remote: conan-center
    Creation date: 2020-01-07 17:01:29
    Required by:
        openssl/1.0.2t

Or generate a graph of your dependencies using Dot or HTML formats:

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

Searching Packages

The remote repository where packages are installed from is configured by default in Conan. It is called Conan Center (configured as conan-center remote).

If we search for something like open in ConanCenter we could find different packages like:

openal/1.18.2@bincrafters/stable
openal/1.19.1
opencv/2.4.13.5@conan/stable
opencv/3.4.3@conan/stable
opencv/4.1.1@conan/stable
openexr/2.3.0
openexr/2.3.0@conan/stable
openexr/2.4.0
openjpeg/2.3.0@bincrafters/stable
openjpeg/2.3.1
openjpeg/2.3.1@bincrafters/stable
openssl/1.0.2s
...

As you can see, some of the libraries end with a @ symbol followed by two strings separated by a slash. These fields are the user and channel for the Conan package, and they are useful if you want to make specific changes and disambiguate your modified recipe from the one in the Conan Center or any other remote. These are legacy packages, and the ones without user and channel are the ones strongly recommended to use from ConanCenter.

ConanCenter is the central public repository for Conan packages. You can contribute packages to it in the conan-center-index Github repository. If you want to store your own private packages, you can download the free Artifactory Community Edition (CE) directly from the Conan downloads page.

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.

A profile needs to be available prior to running commands such as conan install. When running the command, your settings are automatically detected (compiler, architecture…) and stored as the default profile. You can edit these settings ~/.conan/profiles/default or create new profiles with your desired configuration.

For example, if we have a profile with a 32-bit GCC configuration in a file called gcc_x86, we can run the following:

$ conan install .. --profile=gcc_x86

Tip

We strongly recommend using Profiles and managing them with conan config install.

However, the user can always override the profile settings in the conan install command using the --settings parameter. As an exercise, try building the 32-bit version of the hash calculator project like this:

$ conan install .. --settings arch=x86

The above command installs a different package, using the --settings arch=x86 instead of the one of the default profile used previously. Note you might need to install extra compilers or toolchains in some platforms, as for example, Linux distributions no longer install 32bits toolchains by default.

To use the 32-bit binaries, you will also have to change your project build:

  • In Windows, change the CMake invocation to Visual Studio 14.
  • In Linux, you have to add the -m32 flag to your CMakeLists.txt by running SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -m32"), and the same applies to CMAKE_C_FLAGS, CMAKE_SHARED_LINK_FLAGS and CMAKE_EXE_LINKER_FLAGS. This can also be done more easily, by automatically using Conan, as we’ll show later.
  • In macOS, you need to add the definition -DCMAKE_OSX_ARCHITECTURES=i386.

Got any doubts? Check our FAQ, write us or join the community in Cpplang Slack #conan channel!