Outline:

  • Introduction (This one)
  • Package Managers (conan) and Build systems (cmake)
  • C++ Computer vision demo projects: Haar and HOG (added to git repo and referenced here).
  • Visual search & recommendation engine for ExaScale

Introduction

C++ is a powerful programming language that can be used for a wide range of applications, including AI. One of the reasons why it is well-suited for these tasks is that it offers a high level of control over the underlying hardware, which can be important for optimizing performance on edge devices and embedded systems. C++ language, on low-power edge devices, allows for more efficient use of memory and other resources on devices with limited resources. Additionally, C++ has a rich set of libraries and frameworks that can be used for machine learning and other AI-related tasks, such as PyTorch, TensorFlow, Faiss, dlib, OpenCV, and many more.

To complement the rapid development of AI systems we have a plethora of libraries available in the C++ ecosystem. Here is a list (not exhaustive) of some C++ libraries for AI development:

  1. TensorFlow: https://github.com/tensorflow/tensorflow
  2. PyTorch: https://github.com/pytorch/pytorch
  3. dlib: https://github.com/davisking/dlib
  4. Eigen: https://github.com/eigenteam/eigen-git-mirror
  5. OpenCV: https://github.com/opencv/opencv
  6. CatBoost: https://github.com/catboost/catboost
  7. ArmNN: https://github.com/Arm-software/ArmNN
  8. lightgbm: https://github.com/microsoft/LightGBM
  9. mlpack: https://github.com/mlpack/mlpack
  10. Faiss: https://github.com/facebookresearch/faiss
  11. shogun: https://github.com/shogun-toolbox/shogun
  12. GRT (Gesture Recognition Toolkit): https://github.com/nickgillian/grt
  13. MXNet: https://github.com/apache/incubator-mxnet
  14. Armadillo: http://arma.sourceforge.net/
  15. MLPACK: https://github.com/mlpack/mlpack
  16. XGboost: https://github.com/dmlc/xgboost
  17. Shark: https://github.com/Shark-ML/Shark
  18. CNTK: https://github.com/Microsoft/CNTK
  19. ONNX: https://github.com/onnx/onnx

There are many other libraries and framworks, however, some of them are not in active development or have been merged/included with the popular frameworks mentioned above.

For example, PyTorch (LibTorch) is written in C++, this is designed to address the use cases where the use of the Python is infeasible due to performance and portability requirements, such as in low latency, high performance or multithreaded environments, such as embedded systems, video games or production servers. With LibTorch, ML engineers can build and deploy their models in C++ environments, such as native mobile and embedded systems, or in multithreaded environments with strict latency requirements.

Project setup for a dummy project

I will use a simple structure for this application. Here is the output of the tree command to get the folder structure (pre-build stage)

|____APP
	 |____application.cpp
	 |____application.h
	 |____CMakeLists.txt
	 |____conanfile.txt

Conan

Conan is a package manager for C++. It is used to manage and distribute dependencies in your C++ projects. To install Conan, you need to have Python installed on your system (I am using python 3.9). Conan provides packages via Conan center, which is a repository of prebuilt binaries for various machine architectures, that the Conan python client uses to download the required packages.

Here are the steps to install Conan on your system:

  1. Install the Conan CLI: You can install Conan using pip, which is the Python package manager. To do this, open the terminal and run the following command: 
    pip install conan
  2. Configure Conan: After installing Conan, you need to configure it to work with your system. You can do this by running the following command:
conan config install
  1. Add remote repository: By default, Conan doesn’t have any remote repositories to search packages. You can add a remote repository to search packages. For example, you can add the Conan center repository, which is the default public repository for Conan packages, by running the following command:
conan remote add conan-center https://center.conan.io

For more details about Conan check the Jfrog’s conan course and/or Conan documentation.

setting conanfile.txt:

To use Conan in your project, you need to create a conanfile.txt file in our project root directory. This file will contain information about your project’s dependencies (open cv and dlib). Here’s an example conanfile.txt:

[requires]
opencv/4.5.5

[generators]
cmake

Note: I only have opencv as a dependency; getting dlib to work with my Mac M1 Pro was problematic. I had to install dlib from source- check the instruction in dlib repo. For other architecture types, you should be able to specify dlib dependency in the conanfile.txt. Here is how I built and installed dlib.

git clone git@github.com:davisking/dlib.git
cd dlib
mkdir build && cd build
cmake ..
cmake --build .
make install

cmake

setting CMakeLists.txt

To use the cmake build system in your project you need to create a CMakeLists.txt file in your project root directory. This file will contain information about your project’s dependencies. Here’s an example of CMakeLists.txt:

cmake_minimum_required(VERSION 2.8.12)
project(APP)

# C++ 20 standard
add_compile_options(-std=c++20)


if(NOT CMAKE_BUILD_TYPE)
set(CMAKE_BUILD_TYPE Release)
endif()

set(CMAKE_CXX_FLAGS "-Wall -Wextra")
set(CMAKE_CXX_FLAGS_DEBUG "-g")
set(CMAKE_CXX_FLAGS_RELEASE "-O3")

find_package(dlib REQUIRED)  
# Using the "cmake" generator
include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup(TARGETS)

add_executable(app application.cpp)

target_link_libraries(app CONAN_PKG::opencv dlib::dlib)

Note: I use find_package in CMakeList to find and reference the dlib package I built in the previous step. This step is not needed if you were able to install dlib using the Conan package manager, and in that case, you may have to add CONAN_PKG::dlib reference in the target_link_libraries; if not already done so by Conan. This can be controlled in Conan, see conan generators.

In this writeup, I give a basic overview of how to install conan, use Conan, and use CMake build system. For more details, you can refer to CMake and Conan documentations. Moreover, there are many other package managers (vcpkg, hunter etc.) and build systems (bazel, ninja etc.) for C++ development. I am just going over one particular combination of a package manager and a build system (albeit, a popular one) to set up some demo projects, which I have put in my git repo.

Building and running projects

I will take the example of the haar project in the above-mentioned repository. However, the build instructions are mentioned for each project in the corresponding readme.md.

Compiling haar C++ program

Go into the haar folder and type:

mkdir build && cd build
conan install ..
cmake ..
cmake --build .

This will build the program. Sometime, you might need to install packages with conan install .. --build=missing option enabled, when precompiled binaries are not available in the conan-center (remote repository).

Running the program Download the pre-trained cascade detector for the opencv git repo. The opencv repo has many pre-trained haar detectors and I am using one of those in the example below.

You can run the haar program from the build folder while passing the pre-trained haar cascade file with the path.

For example:

bin\haar haarcascade_frontalcatface.xml

[Coming NEXT…]the Exascale AI project using Modern CPP.