Clang 7 <filesystem> 在 Ubuntu 18.04 上找不到标头

Question

我写了CMakeLists.txt文件，如下所示，用于使用 C++17 <filesystem>。这些是其中的一部分。

cmake_minimum_required(VERSION 3.14)
...
list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
include(functions)
include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup()
enable_cxx_compiler_flag_if_supported("-Wall")
enable_cxx_compiler_flag_if_supported("-pedantic")
...
set(Boost_USE_STATIC_LIBS ON)
set(Boost_USE_STATIC_RUNTIME ON)
find_package(Boost 1.65.1 COMPONENTS filesystem regex system thread)
if(Boost_FOUND)
    add_executable(daemon 
                ...)
    target_compile_features(daemon PRIVATE cxx_std_17)
    target_include_directories(daemon PRIVATE ...)
    target_link_libraries(daemon ${Boost_LIBRARIES}) 
    # OS specific instructions.
    if(APPLE)
        find_library(CoreFoundation CoreFoundation)
        find_library(IOKit IOKit)
        target_link_libraries(daemon ${CoreFoundation} ${IOKit}) 
    elseif(WIN32)
        # Windows developer environment specific instructions.
        if(MINGW)
        elseif(MSYS)
        elseif(CYGWIN)
        endif()
    elseif(UNIX)
        // The problem is here. Why Clang cannot find <filesystem>???
        target_link_libraries(daemon c++fs dl)
    else()
    endif()
endif()

我已经尝试了target_link_libraries(daemon stdc++fs dl)和set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -stdlib=libc++ -lc++abi")但没有奏效。

错误代码为

cmake --build .
[1/2] Building CXX object CMakeFiles/daemon.dir/src/thread/serial_manager.cpp.o
FAILED: CMakeFiles/daemon.dir/src/thread/serial_manager.cpp.o 
/usr/bin/clang++   -I/home/koriel/.conan/data/boost/1.65.1/conan/stable/package/f410c60ac3ae66f96115aab74b1c5fbc1a6a4a45/include -I/home/koriel/.conan/data/bzip2/1.0.6/conan/stable/package/abc45b7dce3f5194dea2377c33229fa4f20706b4/include -I/home/koriel/.conan/data/zlib/1.2.11/conan/stable/package/abc45b7dce3f5194dea2377c33229fa4f20706b4/include -I../include/json -I../include/queue -I../src/base64 -I../src/message -I../src/serial -I../src/thread -Wall -pedantic   -DBOOST_USE_STATIC_LIBS -std=gnu++17 -MD -MT CMakeFiles/daemon.dir/src/thread/serial_manager.cpp.o -MF CMakeFiles/daemon.dir/src/thread/serial_manager.cpp.o.d -o CMakeFiles/daemon.dir/src/thread/serial_manager.cpp.o -c ../src/thread/serial_manager.cpp
../src/thread/serial_manager.cpp:43:10: fatal error: 'filesystem' file not found
#include <filesystem>
         ^~~~~~~~~~~~
1 error generated.
ninja: build stopped: subcommand failed.

Answer 1

尽管<filesystem>包含在官方的libc ++ 7中，但许多发行版并不包含它。

我刚刚看了一下 Xcode 10.2(它也附带了 libc++ 7(，我遇到了同样的故事：安装中缺少 filesystem 标头。

你可以看看你的libc ++安装，它应该在Ubuntu系统的/usr(如果你不知道确切的位置，只需运行find /usr -name cstdint，这将指向该位置(。如果在该文件夹中找不到filesystem标头，您可以使用 boost::filesystem 或在 clang 8 可用时立即安装它。