c++ - MinGW64 和 "conflicting declaration of C function int select(...)"

Question

我正在尝试在 MinGW 上构建 Botan，它实际上是 MinGW-w64 (x86_64-pc-msys)。它在 MinGW 上失败，如下所示。我想我把它减少到 MCVE :

#include <sys/select.h>
#include <winsock2.h>
#include <windows.h>
#include <memory>

int main(int argc, char* argv[])
{
    fd_set fds;
    FD_ZERO(&fds);
    FD_SET(0, &fds);

    timeval tv;
    tv.tv_sec = 5;
    tv.tv_usec = 0;

    int rc = select(1, &fds, NULL, NULL, &tv);

    return 0;
}

结果是:

$ g++ -m64 -pthread -std=c++11 test.cxx -o test.exe
In file included from /usr/include/w32api/winsock2.h:56:0,
                 from test.cxx:2:
/usr/include/w32api/psdk_inc/_fd_types.h:100:2: warning: #warning "fd_set and associated macros have been defined in sys/types.      This can cause runtime problems with W32 sockets" [-Wcpp]
 #warning "fd_set and associated macros have been defined in sys/types.  \
  ^~~~~~~
In file included from test.cxx:2:0:
/usr/include/w32api/winsock2.h:995:34: error: conflicting declaration of C function ‘int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, PTIMEVAL)’
   WINSOCK_API_LINKAGE int WSAAPI select(int nfds,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,const PTIMEVAL timeout);
                                  ^~~~~~
In file included from test.cxx:1:0:
/usr/include/sys/select.h:73:5: note: previous declaration ‘int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, timeval*)’
 int select __P ((int __n, fd_set *__readfds, fd_set *__writefds,
     ^~~~~~

包括<sys/select.h>首先很重要。在 Windows header 之后包含它不会出现问题。包括<memory>很重要。 <memory>包括额外的标题，如 <sys/select.h> ，已经包含在内。

据我所知，问题是由 MinGW header 引起的。它们提供具有两个不同签名的相同功能:

/usr/include/w32api/winsock2.h :

int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, PTIMEVAL)

/usr/include/sys/select.h

int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, timeval*)

问题似乎是最后一个参数。在一种情况下是 PTIMEVAL在另一种情况下是timeval* .这似乎与邮件列表有关，但我不明白我应该做什么:Replace struct timeval usage with PTIMEVAL and define TIMEVAL differently on LP64 .

可能存在一些指针大小问题，详见 What do I have to look out for when porting applications to 64 bit Cygwin? , 但它是 MinGW 代码(而不是 Botan 代码)。

问题是什么，我该如何解决？

---

这是 Botan 的 src/lib/utils/socket/socket.cpp .

这是编译错误:

g++ -fstack-protector -m64 -pthread   -std=c++11 -D_REENTRANT -O3 -momit-leaf-frame-pointer  \
-Wall -Wextra -Wpedantic -Wstrict-aliasing -Wcast-align -Wmissing-declarations  \
-Wpointer-arith -Wcast-qual -Wzero-as-null-pointer-constant -Wnon-virtual-dtor  \
-Ibuild/include -c src/lib/utils/socket/socket.cpp -o build/obj/lib/utils_socket.o
In file included from /usr/include/w32api/winsock2.h:56:0,
                 from src/lib/utils/socket/socket.cpp:35:
/usr/include/w32api/psdk_inc/_fd_types.h:100:2: warning: #warning "fd_set and associated macros have been defined in sys/types.      This can cause runtime problems with W32 sockets" [-Wcpp]
 #warning "fd_set and associated macros have been defined in sys/types.  \
  ^~~~~~~
In file included from src/lib/utils/socket/socket.cpp:35:0:
/usr/include/w32api/winsock2.h:995:34: error: conflicting declaration of C function ‘int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, PTIMEVAL)’
   WINSOCK_API_LINKAGE int WSAAPI select(int nfds,fd_set *readfds,fd_set *writefds,fd_set *exceptfds,const PTIMEVAL timeout);
                                  ^~~~~~
In file included from /usr/include/sys/types.h:68:0,
                 from /usr/include/pthread.h:11,
                 from /usr/lib/gcc/x86_64-pc-msys/6.3.0/include/c++/x86_64-pc-msys/bits/gthr-default.h:35,
                 from /usr/lib/gcc/x86_64-pc-msys/6.3.0/include/c++/x86_64-pc-msys/bits/gthr.h:148,
                 from /usr/lib/gcc/x86_64-pc-msys/6.3.0/include/c++/ext/atomicity.h:35,
                 from /usr/lib/gcc/x86_64-pc-msys/6.3.0/include/c++/memory:73,
                 from build/include/botan/types.h:17,
                 from build/include/botan/internal/socket.h:11,
                 from src/lib/utils/socket/socket.cpp:8:
/usr/include/sys/select.h:73:5: note: previous declaration ‘int select(int, _types_fd_set*, _types_fd_set*, _types_fd_set*, timeval*)’
 int select __P ((int __n, fd_set *__readfds, fd_set *__writefds,
     ^~~~~~
make: *** [Makefile:1066: build/obj/lib/utils_socket.o] Error 1

Answer 1

I'm trying to build Botan on MinGW, which is really MinGW-w64 (x86_64-pc-msys)

我怀疑这是错误的目标——您无意中为 MSYS2 环境本身构建，这确实是 POSIXy。这就是为什么例如<sys/select.h>被拉进来引起冲突。至少，我严重怀疑你会尝试使用 <winsock2.h>或 <windows.h>如果您打算构建仅在 MSYS2 环境中使用。您应该确保您从命令行正确调用了 MSYS/使用了正确的快捷方式，以便您配置为为 MINGW64 构建，或者，如果您是，请确保您实际上已经为 MINGW64 安装了 gcc 工具链。如果没有，那么即使您已正确打开 MINGW64，它也会默默地默认返回 MSYS2 的 gcc 工具链，它将继续引入特定于 MSYS2 构建的包含。可以通过运行安装(或重新安装)MINGW64 的 GCC

pacman -Sy mingw-w64-x86_64-gcc

您还可以安装或重新安装特定于 Windows 的 header :

pacman -Sy mingw-w64-x86_64-headers-git 

完成此操作后，运行 uname确认您处于正确的构建环境中，这应该会产生

MINGW64_NT-10.0-18363

然后 gcc -dumpmachine , 这应该产生

x86_64-w64-mingw64

对于 MSYS2，这些值将是

MSYS_NT-10.0-18363

和

x86_64-pc-msys

分别。

为什么我知道这个？从字面上看，我因为同样的问题整夜未眠，直到注意到 _WIN32 和 _WIN64 未定义，以及包含文件的来源( /usr/include ，而不是 /mingw64/x86_64-w64-mingw32/include )，我才意识到我正在为 x86_64-pc-msys 而不是 x86_64-w64-mingw32 构建。

(当然，如果你想为 32 位 Windows 构建，以上所有内容也适用。确保你已正确调用 MINGW32 环境，并且你已运行 pacman -Sy mingw-w64-i686-gcc mingw-w64-i686-headers-git，所以你不要最终尝试使用为 MSYS2 配置的 gcc 进行构建。)

无论如何，鉴于这个问题已有两年历史，我敢肯定，OP 已经开始了。但这是一个容易犯的配置错误。所以，无论如何，我希望这会有所帮助!不要误会我的错误!大家注意安全!