using httplib cmake target

Hi,
I am having a problem with linking httplib library to my project.
I have built httplib and installed it in a certain destination

My CMakeList.txt contains:

find_package(httplib CONFIG REQUIRED)
...
add_executable(${PROJECT_NAME} ${SRC})
target_link_libraries(${PROJECT_NAME} PUBLIC httplib)

This works, and the Cmake cache contains valid entry for httplib_DIR where the httplibConfig.cmake is located. But when I try to compile my project, it can't find the httplib.h, which I include. I looked into httplibConfig.cmake and there is created an INTERFACE target httplib (without any namespace), so I believe linking targets it the way I did should be enough to pass all directories. Could you please point out what is missing?

@guteksan

@guteksan, thank you for the feedback. Did you install httplib via CMakeLists.txt in this project? If so, this CMakeLists.txt has been contributed by other user, and I am not familiar to what it actually do (, even I am thinking of removing the file from this project).

Since this library is a 'header-only' library, it doesn't need to link anything. So once you manually copy httplib.h to one of include directories in your system, it much be compiled without any other treatment.

Hope it help!

@yhirose

Hi, @yhirose , thank you for prompt reply.
Yes, I did use CMakeLists.txt from this project to build and install the library. It went smooth, so I thought it is the right way,
I know that header only libraries do not need to be linked, anyway I always prefered to separate my original code from the 3rd party dependencies, and using targets installed in the system is a nice way to do it. You might want to have a look at the Eigen library, which is also header only and allows to be used as targets in own projects.

@guteksan

@guteksan, if "It went smooth, so I thought it is the right way" is true, what do you think causes the problem, in CMakeLists.txt in cpp-httplib, or the one in your project?

Since I don't need the CMakeLists.txt at all and even tested it, I am tending to remove it from this repo unless it doesn't cause any problem...

Header only libraries on cmake are not linked against. Instead target_include_directory is used with the package directory.

@PixlRainbow

@PixlRainbow: not exactly. I am not talking about linking in a proper sense, but about linking in a cmake buildsystem sense. Cmake has a concept of targets which combine information about both libs and include directiories, and the proper way of adding the dependency to a target is by: target_link_libraries, even if this is header only library. CMakeLists.txt attached to a project created a target named httplib, so that method should be used. Out of curiosity I checked if target_include_directiories will work on httplib target, but it didn't.

@guteksan

@guteksan, if the current CMakeLists.txt has the problem, I'll get rid of it from this project because I don't use it anyway and I am not planning to maintain it. I would like to avoid confusing to the users.

If you think it's still useful and find the cause of the problem, please submit a pull request. Of course, that would be the best for me! Thanks for your understanding.

Removed CMakeLists.txt. (Fix #421)

Could you consider bringing the file back? Having a Cmake file available is nice, even for header-only. It also affects the Conan package (at least future versions).

The problem was probably where it installed to. For example, it was installing to /usr/include/httplib/httplib.h on Linux, but I'm assuming the OP was doing #include <httplib.h>. I personally tested v0.5.9, and it worked as-is with only a change to #include <httplib/httplib.h>.

If you wish, I could submit a fix so it's just #include <httplib.h>, as well as some improvements upon the file, considering the file is missing some important things (opt. deps like openssl or zlib, threads, versioning).