Cross-platform C/C++ Development with Conan
Tags: cpp, conan, beginners, tooling
Published: 2021-03-13 17:52:44

Conan is an open source and multi-platform package manager to create and share native binaries (mostly C and C++). It is written in Python and supports Windows, Linux, and Mac.

Besides managing dependencies, conan simplifies development process by integrating with various build tools. I touched on its most basic usage in tandem with cmake in my previous blog-post titled ["Building HTTP Service in C++"](https://dev.to/aakatev/building-http-service-in-c-using-modern-tools-14af). However, that post aimed primary towards Mac and Linux users, and developers using Windows platform were left aside.

Today, let's see how we can use conan to manage cross-platform development.

Let's start by creating a conanfile. Instead of using plaintext file, like in the HTTP service post, we use a Python script. Conan has ability to work with both types.

**conanfile.py**

```python
from conans import ConanFile, CMake, tools

class MyApp(ConanFile):
    name = "my_app"
    version = "1.0"
    license = "unlicensed"
    author = "Artem Akatev"
    settings = "os", "compiler", "build_type", "arch"
    options = {"shared": [True, False], "fPIC": [True, False]}
    default_options = {"shared": False, "fPIC": True}
    generators = "cmake"
    requires = "boost/1.75.0"

    def config_options(self):
        if self.settings.os == "Windows":
            del self.options.fPIC
    
    def build(self):
        cmake = CMake(self)
        cmake.configure(source_folder="src")
        cmake.build()
```

Two important directives in the file are `generators` and `requires`. The first one contains a list of build tools, and the second a list of all dependencies. Both lists are comma delimited.

The build section (Python function) contains cmake configuration. The cmake is set to expect `CMakeLists.txt` file in src folder, so let's create the file.

**src/CMakeLists.txt**

```cmake
cmake_minimum_required(VERSION 2.8.12)
project(my_app)

add_definitions("-std=c++11")

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

add_executable(my_app main.cc)
target_link_libraries(my_app ${CONAN_LIBS})
```

Now we need some application to compile. I will "steal" [an example of HTTP client](https://www.boost.org/doc/libs/1_75_0/libs/beast/example/http/client/sync/http_client_sync.cpp) from Boost Beast.

```c++

#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/connect.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <cstdlib>
#include <iostream>
#include <string>

namespace beast = boost::beast;     // from <boost/beast.hpp>
namespace http = beast::http;       // from <boost/beast/http.hpp>
namespace net = boost::asio;        // from <boost/asio.hpp>
using tcp = net::ip::tcp;           // from <boost/asio/ip/tcp.hpp>

// Performs an HTTP GET and prints the response
int main(int argc, char** argv)
{
    try
    {
        // Check command line arguments.
        if(argc != 4 && argc != 5)
        {
            std::cerr <<
                "Usage: http-client-sync <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
                "Example:\n" <<
                "    http-client-sync www.example.com 80 /\n" <<
                "    http-client-sync www.example.com 80 / 1.0\n";
            return EXIT_FAILURE;
        }
        auto const host = argv[1];
        auto const port = argv[2];
        auto const target = argv[3];
        int version = argc == 5 && !std::strcmp("1.0", argv[4]) ? 10 : 11;

        // The io_context is required for all I/O
        net::io_context ioc;

        // These objects perform our I/O
        tcp::resolver resolver(ioc);
        beast::tcp_stream stream(ioc);

        // Look up the domain name
        auto const results = resolver.resolve(host, port);

        // Make the connection on the IP address we get from a lookup
        stream.connect(results);

        // Set up an HTTP GET request message
        http::request<http::string_body> req{http::verb::get, target, version};
        req.set(http::field::host, host);
        req.set(http::field::user_agent, BOOST_BEAST_VERSION_STRING);

        // Send the HTTP request to the remote host
        http::write(stream, req);

        // This buffer is used for reading and must be persisted
        beast::flat_buffer buffer;

        // Declare a container to hold the response
        http::response<http::dynamic_body> res;

        // Receive the HTTP response
        http::read(stream, buffer, res);

        // Write the message to standard out
        std::cout << res << std::endl;

        // Gracefully close the socket
        beast::error_code ec;
        stream.socket().shutdown(tcp::socket::shutdown_both, ec);

        // not_connected happens sometimes
        // so don't bother reporting it.
        //
        if(ec && ec != beast::errc::not_connected)
            throw beast::system_error{ec};

        // If we get here then the connection is closed gracefully
    }
    catch(std::exception const& e)
    {
        std::cerr << "Error: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

```

Next, open a terminal window in the project's root directory (same as the directory containing `conanfile.py`), and follow these steps to build and run the application:

**1. Install build dependencies**

```sh
conan install . --install-folder build
```

**2. Build binary**

```sh
conan build . --build-folder build
```

**Run your application**

Mac and Linux

```sh
./build/bin/my_app google.com 443
```

Windows

```cmd
build\bin\my_app.exe google.com 443
```