Implicit declaration of function 'getaddrinfo' on MinGW

问题

I have a C program that uses getaddrinfo(). It works as expected on Linux and Mac OS X.

I'm in the middle of porting it to Windows.

When I compile it (with MinGW gcc) I get the following warnings:

ext/socket/socket.c: In function 'sl_tcp_socket_init':
ext/socket/socket.c:98:5: warning implicit declaration of function 'getaddrinfo' [-Wimplicit-function-declaration]
ext/socket/socket.c:104:9: warning implicit declaration of function 'freeaddrinfo' [-Wimplicit-function-declaration]

Then the entire thing fails to link with undefined references to getaddrinfo() and freeaddrinfo().

Now, according to this MSDN page, getaddrinfo() is supported on Windows and is located in the header file Ws2tcpip.h and the library file Ws2_32.lib.

I'm including Ws2tcpip.h and linking with -lWs2_32, so I'm not sure why this isn't working.

回答1:

If you have a look at line 297 of ws2tcpip.h, you can see that there's a check of the value of _WIN32_WINNT.

#if (_WIN32_WINNT >= 0x0501)
void WSAAPI freeaddrinfo (struct addrinfo*);
int WSAAPI getaddrinfo (const char*,const char*,const struct addrinfo*,
                struct addrinfo**);
int WSAAPI getnameinfo(const struct sockaddr*,socklen_t,char*,DWORD,
               char*,DWORD,int);
#else
/* FIXME: Need WS protocol-independent API helpers.  */
#endif

Just #define _WIN32_WINNT before your includes.

回答2:

If you want to make your code compiler-wide you should actually also define NTDDI_VERSION with the same OS version as _WIN32_WINNT. Without that defining only _WIN32_WINNT will not let you to use getaddrinfo() with some compilers (i.e. Watcom). It is better to wrap it in the same way as Windows SDK does:

#define _NTDDI_VERSION_FROM_WIN32_WINNT2(ver)    ver##0000
#define _NTDDI_VERSION_FROM_WIN32_WINNT(ver)     _NTDDI_VERSION_FROM_WIN32_WINNT2(ver)

#ifndef _WIN32_WINNT
#  define _WIN32_WINNT 0x501
#endif
#ifndef NTDDI_VERSION
#  define NTDDI_VERSION _NTDDI_VERSION_FROM_WIN32_WINNT(_WIN32_WINNT)
#endif