CMake target nlohmann_json does not have src into its interface includes

[sogartar]

If you do in CMake:

add_subdirectory(nlohmann/json)
target_link_libraries(my_target PRIVATE nlohmann_json)

Then my_target does not have nlohmann/json/src into its includes, where json.hpp is. You can not properly include this project into other CMake projects.
Note that in v2.1.1 it used to be OK.

[nlohmann]

maybe related: #695

[dan-42]

@sogartar what system do you use? Windows? Mac? Linux?
have you installed it first via?

cmake
make
make install

If the usage you described is a common one (I did never useed 3rdparty CMake-Projekts like this)
Then indeed this might be a BUG.
Please not that the up comming version V3.0.0 will bring breaking changes including the usage of build-tools and package-managers. see #698

[dan-42]

@sogartar I forgot, a simpler oneliner for your case could be

include_directory(nlohmann/json/src)

[nlohmann]

Is there anything to be done to close this issue?

[sogartar]

I think you should add nlohmann/json/src to the public includes of the nlohmann_json target. See target_include_directories.

[dan-42]

Well @sogartar thx for answering any of my questions. so IMHO I would ignore it.

But I will have a look and see what impact the suggestion would be.

[nlohmann]

Does anyone has an idea how to proceed here?

[nlohmann]

Issue #790 also proposes to change the include dir.

[nlohmann]

Sorry, #790 is unrelated to this issue.

[nlohmann]

I need more info on this issue. What needs to be fixed? Is there example code to demonstrate the issue?

[theodelrieu]

Playing with target_include_directories and generator expressions should do the trick.

I'll open a PR tomorrow morning.

[pfaco]

I think there is still some problem in the include directories.

I installed the lib with the following commands:

cmake -DCMAKE_INSTALL_PREFIX=C:/cmake -G "Unix Makefiles"
make install

So I got the lib at C:/cmake/include/nlohmann/json.hpp
and the cmake files at C:/cmake/lib/cmake/nlohmann_json

My cmake project is really simple:

cmake_minimum_required(VERSION 3.10)
project(test_cpp)

set(CMAKE_CXX_STANDARD 17)

find_package(nlohmann_json 3.1.2)

add_executable(test_cpp main.cpp)

target_link_libraries(test_cpp PRIVATE nlohmann_json)

The find_package and target_link_libraries commands work well.
When trying to include the header it doesn't work (cannot find the header).
I tried the following without success:
#include <nlohmann/json.hpp>
#include <json.hpp>

I'm not so experienced with cmake so I might be doing something wrong, although I have successfully used many other libraries following the same procedure.

Any sugestions on how to tackle this? @dan-42 @theodelrieu

[theodelrieu]

Could you try nlohmann_json::nlohmann_json? The target should be inside a namespace IIRC.

[pfaco]

Could you try nlohmann_json::nlohmann_json? The target should be inside a namespace IIRC.

Yes, that solved it! Just added nlohmann_json::nlohmann_json to the target_link_libraries command. Thanks!