How to use C++ libraries?

Question

I am a Python developer and I have not used C++ since university. I am doing scientific programming with python, mainly. I wanted to try C++ to see if it is better performance-wise.

I am quite new in C++. I have found dlib library, which seemed a good library as it had many interesting features. But when I downloaded it, I found several folder full of .h and .cpp files.

In Python, I would have installed a wanted library using pip or something, then use it in my project using import.

Is there a similar installation for c++ libraries? Or do I have to look among all those .h and .cpp files and decide which ones I need in my project then copy them? Or how do I use the dlib library?

I have searched a lot on google but I could not find any indication on how to use a c++ library or install a new package to be used.

I use Visual Studio Community 2017 and Windows 10 if that matters.

Answer 1

To integrate a library, you need two kinds of things:

• header files (usually *.h) with the declarations required to let the compiler know about the features in the library (a little similar to an import statement);

• compiled library files (usually *.lib) containing the precompiled executable code itself, to let the linker assemble the final executable file.

In some cases (especially for templated code), a library can be made of header files only. In other cases, the package doesn't contain a ready-made library file and you have to build it yourself or manually include the source files (*.c/cpp) in your project.

Not speaking of the innumerable optional settings that you may have to adjust to comply with the specifics of the generated code, such as function calling convention, struct alignment...

Last but not least, some libraries are connected to at run-time only. They are called Dynamic Link Libraries and involve yet different procedures.

All of this is relatively complex and close to black magic for beginners. If you are very lucky, you will find some library documentation telling you which options to use for your compiler. If you can, start from an existing sample project that works!

For dlib, check http://dlib.net/compile.html.

Be ready for a cultural shock when you will compare to the ease of use of the Python modules.

Answer 2

It is quite a broad question, but I'll do my best.

First of all, in C++ libraries consist of header files and precompiled part (.lib,.dll on Windows, .a, .so on Linux). To use them in your project you have to inform your program (and compiler) about features that library has (by #including their header file) and linker to include that library binaries.

pip is package manager, which automatically downloads, builds and installs library that you want in your system. In C++ there is no such single tool at the moment and there steps must be done more or less manually.

For dowloading you usually end up with git or downloading the zip archive with source (do it here). Once you have sources you have to build it.

In order to achieve multiplatformity libraries usually does not get shipped with concrete build system description (Visual Studio Project on Windows or makefile on Linux etc.), but are created in more general tool CMake, which abstracts them. E.g. dlib does that. With use of CMake (For start I recommend CMake-GUI, which is installed with CMake on Windows) you can generate Visual Studio Project, which later you can open and compile to generate .lib file. How exactly to do it follow dlib compilation description.

Once you have you lib and headers files on your disk you can add headers and .lib to your Visual Project and use as any other C++ library. (Seems old, but should work)