Cannot linking cmake targets

Question

I have the following structure of my project:

Project
-- CMakeLists.txt
-- src/
-- -- main.cpp
-- include/
-- -- curl/
-- -- -- *.h files
-- -- nlohmann/
-- -- -- *.hpp files
-- lib/
-- -- libcurl.lib

Project/CMakeLists:

cmake_minimum_required(VERSION 3.1)
set(PROJECT_NAME "VKAPI")
project(${PROJECT_NAME} CXX)

include_directories(${PROJECT_SOURCE_DIR}/include)

file(GLOB TARGET_SRC "./src/*.cpp")

add_executable(main ${TARGET_SRC})
target_link_libraries(main "${CMAKE_SOURCE_DIR}/lib/libcurl.lib")

install(TARGETS main DESTINATION bin)

It works fine, but when I launch main.exe, it doesn't work. Instead of executing correctly and displaying the message, it ends with the code 0. Code:

#include <iostream>

#include "curl/curl.h"
#include "nlohmann/json.hpp"

int main()
{
    CURL* curl = curl_easy_init();

    std::cout << "That's work!" << std::endl;
    std::cout << "Hello Easy C++ project!" << std::endl;
}

But when I delete "#include "curl/curl.h"" and "#include "nlohmann/json.hpp"", it started to work fine.

Maybe this thread help [link](https://stackoverflow.com/questions/16655705/cmake-cannot-determine-linker-language-for-target) — arsham belivani, Jul 26 '20 at 07:31
`TARGET_CURL "./*.h")` curl target has only headers. Headers don't mean much. So is this curl target a C++ or C project? Note that you are not linking _libraries_ but _cmake targets_. — KamilCuk, Jul 26 '20 at 07:39
https://stackoverflow.com/questions/11801186/cmake-unable-to-determine-linker-language-with-c second asnwer — KamilCuk, Jul 26 '20 at 07:51
No? Doing `set_target_properties(curl PROPERTIES LINKER_LANGUAGE CXX)` and similar for nlo-something should have worked. — KamilCuk, Jul 26 '20 at 08:03
@KamilCuk, it didn't help me too. I decided to rewrite CMakeLists, check updates. — qucals, Jul 26 '20 at 08:40
Please see the responses [here](https://stackoverflow.com/questions/8774593/cmake-link-to-external-library) for how to properly link external libraries using CMake. — Kevin, Jul 26 '20 at 12:16

score 0 · Answer 1 · answered Jul 26 '20 at 08:03

0

This:

file(GLOB TARGET_HEADERS "*.hpp")

add_library(nlohmann ${TARGET_HEADERS})

Is wrong in two ways:

You should not glob your sources, you should list them explicitly. There is plenty of guidance on this written already, globbing is a no-no in CMake.
Your "library" does not contain any source code. A library in CMake requires source code such as a .c or .cpp file to compile. You actually don't need to mention the header files at all, just tell CMake about the files it needs to compile, not the headers.

answered Jul 26 '20 at 08:03

John Zwinck

239,568
38
324
436

I suggest, I need to do next: include_directories(./include/) target_link_libraries(main "./lib/libcurl.lib") and remove others cmakelists (curl & nlohmann)? – qucals Jul 26 '20 at 08:34
Yes, something like that. – John Zwinck Jul 26 '20 at 08:53

score 0 · Accepted Answer · answered Jul 26 '20 at 11:08

0

My error in the line: target_link_libraries(main "${CMAKE_SOURCE_DIR}/lib/libcurl.lib") It worked when I added a word INTERFACE: target_link_libraries(main INTERFACE "${CMAKE_SOURCE_DIR}/lib/libcurl.lib")

answered Jul 26 '20 at 11:08

qucals

27
7

Cannot linking cmake targets

2 Answers2