CODEWITHSUNDEEP
c++githubcmakevisual-studio-2017
jp94
jp94

Reputation: 325

How to use an external library for C++ in VS2017

I've been programming in Python for over a year now but am just learning C++ and am unfamiliar with how to go about using external libraries, CMake and github for that matter. I'm trying to use an external library called cpr - https://github.com/whoshuu/cpr. So far I've followed the instructions in the 'Usage' section of that link up to, but not including, the "add_subdirectory(cpr)" bit.

So far I've got the source code for cpr in the Visual Studio project folder of my C++ project. In the project properties I've then added into Include Directories (under VC++ Directories) "$(SolutionDir)site_libs\cpr\include" and I've added the same thing into Additional Include Directories (under C/C++ -> All Options). This means that the following code compiles just fine:

 #include <cpr/cpr.h>

int main(int argc, char** argv) {
    auto r = 
cpr::Get(cpr::Url{"https://api.github.com/repos/whoshuu/cpr/contributors"},
                      cpr::Authentication{"user", "pass"},
                      cpr::Parameters{{"anon", "true"}, {"key", "value"}});
    r.status_code;                  // 200
    r.header["content-type"];       // application/json; charset=utf-8
    r.text;                         // JSON text string
}

However this code isn't working when it comes to building, due to link errors. I'm pretty sure the thing I'm missing is the actual .lib file for it to find where these functions etc are defined (nothing for cpr is set in the Linker -> Input property). So I'm wondering - how do I create this .lib file / is that even the right thing to do / what is this "add_subdirectory(cpr)" and where/how do I run it... basically what do I do to make this whole thing work..?! I've tried compiling cpr with CMake but it throws a load of errors about 'CMakeLists.txt' not present in certain folders.

Apologies if I've used any incorrect terminology here, only been learning C++ for a couple of days now. Any help massively appreciated!

Upvotes: 1

Views: 2883

Answers (1)

SoronelHaetir
SoronelHaetir

Reputation: 15172

If the library does not come as a binary distribution (that is with the .lib already built) you are going to need to build it as a separate project from the code you want to use the library, that step will build the .lib file. If a .sln is included with the distribution use that otherwise you may well have to create your own (or add it as a project to an existing solution).

Once you have a .lib add the directory under the VC++ directories of the project settings and add the actual .lib file name under Linker->Input on the Additional Dependencies line.

To build the library if the distribution does not include the needed VS files you will need to create a project at minimum (it can be part of the solution for your program), right click on the solution node in solution explorer and select Add->New Project, from there select Visual C++->Windows Desktop and either Dynamic Link Library or Static Library as you desire.

Go to the Project menu and select Project Dependencies, change your program to depend on the new project, this will set build order so your program project builds after the library.

You may need to disable the use of pre-compiled headers, right click on the new project node select Properties, go to C/C++->precompiled headers and change Precompiled Headers->Precompiled Header to Not using precompiled headers.

Next add the header and source files to the project and attempt building.

If this succeeded you will have a .lib suitable for use in the additional dependencies of your program project as already described.

Upvotes: 2

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