C++ 实验性::文件系统链接器错误
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experimental::filesystem linker error
提问by Klaus
I try to use the new c++1z features actually on the head of development within gcc 6.0.
我尝试在 gcc 6.0 中的开发负责人中实际使用新的 c++1z 功能。
If I try this little example:
如果我尝试这个小例子：
#include <iostream>
#include <experimental/filesystem>
namespace fs = std::experimental::filesystem;
int main()
{
fs::path p1 = "/home/pete/checkit";
std::cout << "p1 = " << p1 << std::endl;
}
I got:
我有：
/opt/linux-gnu_6-20151011/bin/g++ --std=c++1z main.cpp -O2 -g -o go /tmp/ccaGzqFO.o: In function \`std::experimental::filesystem::v1::__cxx11::path::path(char const (&) [36])': /opt/linux-gnu_6-20151011/include/c++/6.0.0/experimental/bits/fs_path.h:167: undefined reference to `std::experimental::filesystem::v1::__cxx11::path::_M_split_cmpts()' collect2: error: ld returned 1 exit status
gcc version is the snapshot linux-gnu_6-20151011
gcc 版本是快照 linux-gnu_6-20151011
Any hints how to link for the new c++1z features?
任何提示如何链接新的 c++1z 功能？
回答by Jonathan Wakely
The Filesystem TS is nothing to do with C++1z support, it is a completely separate specification not part of the C++1z working draft. GCC's implementation (in GCC 5.3 and later) is even available in C++11 mode.
Filesystem TS 与 C++1z 支持无关，它是一个完全独立的规范，不属于 C++1z 工作草案的一部分。GCC 的实现（在 GCC 5.3 及更高版本中）甚至可以在 C++11 模式下使用。
You just need to link with -lstdc++fsto use it.
您只需要链接-lstdc++fs即可使用它。
(The relevant library, libstdc++fs.a, is a static library, so as with any static library it should come afterany objects that depend on it in the linker command.)
（相关库 ，libstdc++fs.a是一个静态库，因此对于任何静态库，它应该在链接器命令中依赖于它的任何对象之后。）
Update Nov 2017:as well as the Filesystem TS, GCC trunk now alsohas an implementation of the C++17 Filesystem library, defined in <filesystem>and in namespace std::filesystem(N.B. no "experimental" in those names) when using -std=gnu++17or -std=c++17. GCC's C++17 support is not complete or stable yet, and until it's considered ready for prime time use you also need to link to -lstdc++fsfor the C++17 Filesystem features.
2017 年 11 月更新：除了文件系统 TS，GCC 主干现在还具有 C++17 文件系统库的实现，在使用or时<filesystem>在命名空间中和命名空间中定义std::filesystem（注意这些名称中没有“实验性”）。GCC 的 C++17 支持还不完整或稳定，在它被认为准备好用于黄金时间之前，您还需要链接到C++17 文件系统功能。-std=gnu++17-std=c++17-lstdc++fs
Update Jan 2019:starting with GCC 9, the C++17 std::filesystemcomponents can be used without -lstdc++fs(but you still need that library for std::experimental::filesystem).
2019 年 1 月更新：从 GCC 9 开始，std::filesystem可以不使用C++17组件-lstdc++fs（但您仍然需要该库用于std::experimental::filesystem）。
回答by Searene
If you are using cmake, add the following line to CMakeLists.txt:
如果您使用的是 cmake，请将以下行添加到CMakeLists.txt：
link_libraries(stdc++fs)
So that cmake can link against the corresponding library.
以便 cmake 可以链接到相应的库。
回答by xaxxon
With clang 4.0+, you need to link against libc++experimental.a
使用 clang 4.0+，您需要链接 libc++experimental.a
Make sure you're building with libc++ (not libstdc++) with the -stdlib=libc++ (as mentioned in the comments)
确保您使用 -stdlib=libc++ 使用 libc++（而不是 libstdc++）构建（如评论中所述）
回答by caot
Here is a demo that might be helpful to someone in the future:
这是一个演示，可能对将来的人有所帮助：
env: el6, gcc/5.5.0
环境：el6，gcc/5.5.0
#include <iostream>
#include <string>
#include <experimental/filesystem>
int main()
{
std::string path = std::experimental::filesystem::current_path();
std::cout << "path = " << path << std::endl;
}
The following are compiling and testing. The flags are -std=c++17-lstdc++fs:
以下是编译和测试。标志是-std=c++17-lstdc++fs：
$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/apps/gcc-5.5.0/bin/../libexec/gcc/x86_64-unknown-linux-gnu/5.5.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/apps/gcc-5.5.0 --disable-multilib --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --enable-languages=all
Thread model: posix
gcc version 5.5.0 (GCC)
$ ls -lrt /apps/gcc-5.5.0/lib64 | grep libstdc
-rwxr-xr-x. 1 root root 11272436 Jun 25 10:51 libstdc++.so.6.0.21
-rw-r--r--. 1 root root 2419 Jun 25 10:51 libstdc++.so.6.0.21-gdb.py
-rwxr-xr-x. 1 root root 976 Jun 25 10:51 libstdc++.la
-rwxr-xr-x. 1 root root 11272436 Jun 25 10:51 libstdc++.so
-rw-r--r--. 1 root root 10581732 Jun 25 10:51 libstdc++fs.a
-rw-r--r--. 1 root root 28985412 Jun 25 10:51 libstdc++.a
-rwxr-xr-x. 1 root root 916 Jun 25 10:51 libstdc++fs.la
-rwxr-xr-x. 1 root root 11272436 Jun 25 10:51 libstdc++.so.6
$ g++ filesystem-testing.cpp -lstdc++fs -std=c++17
$ ./a.out
$ g++ -std=c++17 filesystem-testing.cpp -lstdc++fs
$ ./a.out
path = /home/userid/projects-c++/filesystem-testing
It also works with flags: -std=c++11
它也适用于标志： -std=c++11
$ g++ -std=c++11 filesystem-testing.cpp -lstdc++fs
$ ./a.out
path = /home/userid/projects-c++/filesystem-testing
The follows had compiling error _ZNSt12experimental10filesystem2v112current_pathB5cxx11Ev
以下有编译错误 _ZNSt12experimental10filesystem2v112current_pathB5cxx11Ev
$ g++ -std=c++17 -lstdc++fs filesystem-testing.cpp
/tmp/ccA6Q9oF.o: In function `main':
filesystem-testing.cpp:(.text+0x11): undefined reference to `_ZNSt12experimental10filesystem2v112current_pathB5cxx11Ev'
collect2: error: ld returned 1 exit status
