Tutorial: Install and use packages with CMake

Article
09/25/2024

This tutorial shows you how to create a C++ "Hello World" program that uses the fmt library with CMake and vcpkg. You'll install dependencies, configure, build, and run a simple application.

Prerequisites

A terminal
A C++ compiler
CMake
Git

Note

For Windows users, Visual Studio's MSVC (Microsoft Visual C++ Compiler) is the required compiler for C++ development.

1 - Set up vcpkg

Clone the repository

The first step is to clone the vcpkg repository from GitHub. The repository contains scripts to acquire the vcpkg executable and a registry of curated open-source libraries maintained by the vcpkg community. To do this, run:
```
git clone https://github.com/microsoft/vcpkg.git
```
The vcpkg curated registry is a set of over 2,000 open-source libraries. These libraries have been validated by vcpkg's continuous integration pipelines to work together. While the vcpkg repository does not contain the source code for these libraries, it holds recipes and metadata to build and install them in your system.
Run the bootstrap script

Now that you have cloned the vcpkg repository, navigate to the vcpkg directory and execute the bootstrap script:
```
cd vcpkg && bootstrap-vcpkg.bat
```
```
cd vcpkg; .\bootstrap-vcpkg.bat
```
```
cd vcpkg && ./bootstrap-vcpkg.sh
```
The bootstrap script performs prerequisite checks and downloads the vcpkg executable.

That's it! vcpkg is set up and ready to use.

2 - Set up the project

Configure the VCPKG_ROOT environment variable.
```
export VCPKG_ROOT=/path/to/vcpkg
export PATH=$VCPKG_ROOT:$PATH
```
Note

Setting environment variables using the export command only affects the current shell session. To make this change permanent across sessions, add the export command to your shell's profile script (e.g., ~/.bashrc or ~/.zshrc).
```
set "VCPKG_ROOT=C:\path\to\vcpkg"
set PATH=%VCPKG_ROOT%;%PATH%
```
Note

Setting environment variables in this manner only affects the current terminal session. To make these changes permanent across all sessions, set them through the Windows System Environment Variables panel.
```
$env:VCPKG_ROOT = "C:\path\to\vcpkg"
$env:PATH = "$env:VCPKG_ROOT;$env:PATH"
```
Note

Setting environment variables in this manner only affects the current terminal session. To make these changes permanent across all sessions, set them through the Windows System Environment Variables panel.
Setting VCPKG_ROOT tells vcpkg where your vcpkg instance is located. Adding it to PATH ensures you can run vcpkg commands directly from the shell.
Create the project directory.
```
mkdir helloworld && cd helloworld
```

3 - Add dependencies and project files

Create the manifest file and add the fmt dependency.

First, create a manifest file (vcpkg.json) in your project's directory by running the vcpkg new command from within the helloworld directory:
```
vcpkg new --application
```
Next, add the fmt dependency:
```
vcpkg add port fmt
```
Your vcpkg.json should look like this:
```
{
    "dependencies": [
        "fmt"
    ]
}
```
This is your manifest file. vcpkg reads the manifest file to learn what dependencies to install and integrates with CMake to provide the dependencies required by your project.

The default vcpkg-configuration.json file introduces baseline constraints, specifying the minimum versions of dependencies that your project should use. While modifying this file is beyond the scope of this tutorial, it plays a crucial role in defining version constraints for your project's dependencies. Therefore, even though it's not strictly necessary for this tutorial, it's a good practice to add vcpkg-configuration.json to your source control to ensure version consistency across different development environments.
Create the project files.

Create the CMakeLists.txt file with the following content:
```
cmake_minimum_required(VERSION 3.10)

project(HelloWorld)

find_package(fmt CONFIG REQUIRED)

add_executable(HelloWorld helloworld.cpp)

target_link_libraries(HelloWorld PRIVATE fmt::fmt)
```
Now, let's break down what each line in the CMakeLists.txt file does:
- cmake_minimum_required(VERSION 3.10): Specifies that the minimum version of CMake required to build the project is 3.10. If the version of CMake installed on your system is lower than this, an error will be generated.
- project(HelloWorld): Sets the name of the project to "HelloWorld."
- find_package(fmt CONFIG REQUIRED): Looks for the fmt library using its CMake configuration file. The REQUIRED keyword ensures that an error is generated if the package is not found.
- add_executable(HelloWorld helloworld.cpp): Adds an executable target named "HelloWorld," built from the source file helloworld.cpp.
- target_link_libraries(HelloWorld PRIVATE fmt::fmt): Specifies that the HelloWorld executable should link against the fmt library. The PRIVATE keyword indicates that fmt is only needed for building HelloWorld and should not propagate to other dependent projects.
Create the helloworld.cpp file with the following content:
```
#include <fmt/core.h>

int main()
{
    fmt::print("Hello World!\n");
    return 0;
}
```
In this helloworld.cpp file, the <fmt/core.h> header is included for using the fmt library. The main() function then calls fmt::print() to output the "Hello World!" message to the console.

4 - Build and run the project

Run CMake configuration

CMake can automatically link libraries installed by vcpkg when CMAKE_TOOLCHAIN_FILE is set to use vcpkg's custom toolchain. This can be acomplished using CMake presets files.

Create the following files inside the helloworld directory:

CMakePresets.json
```
{
  "version": 2,
  "configurePresets": [
    {
      "name": "vcpkg",
      "generator": "Ninja",
      "binaryDir": "${sourceDir}/build",
      "cacheVariables": {
        "CMAKE_TOOLCHAIN_FILE": "$env{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake"
      }
    }
  ]
}
```
CMakeUserPresets.json
```
{
    "version": 2,
    "configurePresets": [
      {
        "name": "default",
        "inherits": "vcpkg",
        "environment": {
          "VCPKG_ROOT": "<path to vcpkg>"
        }
      }
    ]
  }
```
The CMakePresets.json file contains a single preset named "vcpkg", which sets the CMAKE_TOOLCHAIN_FILE variable. The CMakeUserPresets.json file sets the VCPKG_ROOT environment variable to point to the absolute path containing your local installation of vcpkg. It is recommended to not check CMakeUserPresets.json into version control systems.

Finally, configure the build using CMake:
```
cmake --preset=default
```
Build the project

Run:
```
cmake --build build
```
Run the application

Finally, run the executable to see your application in action:
```
./build/HelloWorld

Hello World!
```
```
.\build\HelloWorld.exe

Hello World!
```

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