CMake flow not forcing c++17 and filesystem library to link

[bentomo]

Bug category

• bug - compilation error
• bug - compilation warning
• bug - runtime error
• bug - runtime warning
• bug - logic error

Describe the bug
I'm already aware of the c++17 requirements but there seems to be a gray area where the std::filesystem library is ACTUALLY included in the c++ version. I had cmake print out the actual compiler command for me and I wasn't seeing stdc++17 or stdc++fs anywhere. Anytime I tried to build the examples or a test project using this I couldn't get it to figure out how to link in file system. I'm putting this here for alter in case anyone else has the same problem as me. I spent WAY too long trying to figure out how to do this properly in the cmake flow, and I'm too stupid to figure that out. I ended up just hacking the cmakefiles to get it to build.

From what I can tell there are a bunch of other issues related to the filesystem flow in this repo so maybe this will help answer some stuff. I'm not sure what the FindFilesystem.cmake file is for either, I couldn't tell when it's supposed to run but I don't think it was.

diff --git a/cmake/functions/link_external_libraries.cmake b/cmake/functions/link_external_libraries.cmake
index c188265..2aa45fd 100644
--- a/cmake/functions/link_external_libraries.cmake
+++ b/cmake/functions/link_external_libraries.cmake
@@ -20,9 +20,9 @@ function(target_link_libraries_system target)
       message("Warning: ${lib} doesn't set INTERFACE_INCLUDE_DIRECTORIES. No include_directories set.")
     endif()
     if(scope)
-      target_link_libraries(${target} ${scope} ${lib})
+      target_link_libraries(${target} ${scope} ${lib} stdc++fs)
     else()
-      target_link_libraries(${target} ${lib})
+      target_link_libraries(${target} ${lib} stdc++fs)
     endif()
   endforeach()
 endfunction(target_link_libraries_system)

Steps to Reproduce

mkdir build
cd build
cmake .. --install-prefix=/home/$USER/matplot_bin -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS="-O2"
make

# or any cmake args really, it seems pretty reproducible with my system, no matter what explatives I yell at my machine it won't use the correct CXX version/library
cmake .. -DCMAKE_RULE_MESSAGES:BOOL=OFF -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++

Output

../../../source/matplot/libmatplot.a(gnuplot.cpp.o): In function `matplot::backend::gnuplot::output(std::__cxx11::basic_string<char, std::char_traits<char>, std::
allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
gnuplot.cpp:(.text+0x1995): undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
gnuplot.cpp:(.text+0x19a4): undefined reference to `std::filesystem::__cxx11::path::parent_path() const'
gnuplot.cpp:(.text+0x1aa1): undefined reference to `std::filesystem::__cxx11::path::parent_path() const'
gnuplot.cpp:(.text+0x1aa9): undefined reference to `std::filesystem::status(std::filesystem::__cxx11::path const&)'
gnuplot.cpp:(.text+0x1ae0): undefined reference to `std::filesystem::__cxx11::path::parent_path() const'
gnuplot.cpp:(.text+0x1ae8): undefined reference to `std::filesystem::create_directory(std::filesystem::__cxx11::path const&)'
gnuplot.cpp:(.text+0x1afd): undefined reference to `std::filesystem::__cxx11::path::parent_path() const'
gnuplot.cpp:(.text+0x1b05): undefined reference to `std::filesystem::status(std::filesystem::__cxx11::path const&)'
gnuplot.cpp:(.text+0x1b41): undefined reference to `std::filesystem::__cxx11::path::parent_path() const'
../../../source/matplot/libmatplot.a(gnuplot.cpp.o): In function `matplot::backend::gnuplot::output(std::__cxx11::basic_string<char, std::char_traits<char>, std::
allocator<char> > const&)':
gnuplot.cpp:(.text+0x3d79): undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
../../../source/matplot/libmatplot.a(gnuplot.cpp.o): In function `std::filesystem::__cxx11::path::extension() const':
gnuplot.cpp:(.text._ZNKSt10filesystem7__cxx114path9extensionEv[_ZNKSt10filesystem7__cxx114path9extensionEv]+0x11): undefined reference to `std::filesystem::__cxx1
1::path::_M_find_extension() const'
gnuplot.cpp:(.text._ZNKSt10filesystem7__cxx114path9extensionEv[_ZNKSt10filesystem7__cxx114path9extensionEv]+0xae): undefined reference to `std::filesystem::__cxx1
1::path::_M_split_cmpts()'
collect2: error: ld returned 1 exit status
make[2]: *** [examples/line_plot/plot/CMakeFiles/example_plot_1.dir/build.make:105: examples/line_plot/plot/example_plot_1] Error 1
make[1]: *** [CMakeFiles/Makefile2:3174: examples/line_plot/plot/CMakeFiles/example_plot_1.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

Platform

• cross-platform issue - linux
• cross-platform issue - windows
• cross-platform issue - macos

Environment Details:

• OS: Red Hat Enterprise Linux
• OS Version: 8.10
• Compiler: gcc/g++
• Compiler version: g++ (GCC) 8.5.0 20210514 (Red Hat 8.5.0-21)

Additional context
I'm attempting to build and install

[alandefreitas]

When this library was written, few compilers had support for <filesystem>, so we needed lots of workarounds. Nowadays, this needs to be refactored, and all the targets need now is target_compile_features(${TARGET_NAME} PRIVATE cxx_std_17).

[bentomo]

Fast response, thanks!

I forgot to include my CMakeLists.txt above. I tried the install method first, but flailed around with some other flows trying to find the right CMake parameters. In the "submodule flow" I had this but the target_compile_features parameter didn't appear to apply to project as a whole. I'm sure it's my CMake ignorance though. I pulled the line plot example code and tried to build it

This yielded the same error.

cmake_minimum_required(VERSION 3.21)
project(plot_test)

add_executable(plot matplot_test.cpp)
target_compile_features(plot PRIVATE cxx_std_17)

add_subdirectory(matplotplusplus)
target_compile_features(matplot PRIVATE cxx_std_17)
target_link_libraries(plot PUBLIC matplot)

[alandefreitas]

Sorry. I wasn't clear. I was talking about what matplot needs to do to solve the problem internally. cxx_std_17 in your project probably won't solve the problem.