Re: [Mingw-users] Undefined reference to 'getaddrinfo'

[James S. <jam...@op...>]

On Thu, 2006-08-24 at 23:20 -0700, Brian Dessent wrote:
> James Steward wrote:
> 
> > I've googled for this for a while now and I'm not sure what to do next.
> 
> Try searching the mailing list archives first.  This has come up before,
> e.g. <http://sourceforge.net/mailarchive/message.php?msg_id=14887873>.
> 
> > When I print the value of _WIN32_WINNT I get 0x400 so obviously the
> > function isn't declared.  That explains the implicit declarations
> > warning.  But what about the undefined references?  The functions are in
> > the library ws2_32.a.
> > 
> > What do I need to do to resolve this?  Is it a MinGW version or a
> > Windows version that needs updating?  Or something completely different?
> 
> The problem, as I described before, is that getaddrinfo() only exists in
> ws2_32 for Windows XP and higher.  If you're willing to generate a
> binary that only runs on XP (and fails with a "Cannot find procedure
> entry point <whatever>" popup box on all other versions) then just do:
> 
> #define WINVER WindowsXP
> 
> ...before including any w32api headers.  This signals that you want the
> feature set of XP, and you don't care about older versions.  Note that
> WindowsXP is defined as 0x0501, and that _WIN32_WINNT gets set to WINVER
> if not already defined, so this is the proper way of declaring this, not
> "#define _WIN32_WINNT 0x0501".
> 
> Now, to complicate things, Microsoft has added support for a
> getaddrinfo() wrapper in their platform SDK, which works only for IPv4,
> as a way of supporting such code on older versions of Windows.  So if
> you are using the platform SDK you can still call getaddrinfo() from
> older versions, but you'll really be just calling the existing
> underlying IPv4 function (gethostbyname() or whatever) and failing if
> you try to use IPv6.
> 
> So, as I said in that reply above, your options are essentially:
> 
> 1. Live with XP-only binary.
> 2. Write (and potentially contribute to the w32api project) a suitable
> getaddrinfo() wrapper for older versions.
> 3. If you're just using IPv4 then call the old standard IPv4 functions
> directly (gethostby*).
> 
> Note that the reason that you got a link error when you did not define
> WINVER is because the getaddrinfo function (and most every Windows API
> function) is declared as type WINAPI which is synonymous with the
> stdcall calling convention, which dictates a function decoration of @nn
> on the end.  But if you call a function without a prototype (as happens
> if you don't set WINVER high enough) then the compiler assumes the
> default cdecl calling convention which does not have that decoration,
> and thus you're trying to call an undecorated function, and the name
> lookup fails at link time.  Another very common way that this plays out
> is that the function actually only exists as FooA and FooW for the ANSI
> and UNICODE variants, but you're meant to call it as just Foo() and the
> include header #defines it to the correct variant based on whether you
> enabled a Unicode build.  Here you get a similar link error if you call
> a function that was not declared in a header.

What a twisted tail...but thanks Brian.  I'll see how I go from here.
An XP only binary might be ok too.  The target platform is XP Pro I
believe.

Cheers,
James.

P.S.  Now I know why I put my hand down when the boss says write some
program for Windows...