Visual Studio 2005 C++ Wrapper unresolved externals

[Michael Abshoff]

Jeremy Rann wrote:
> I've been playing around with GMP a bit, but I've run into some
> difficulty with the C++ wrappers. I'm trying to use GMP in Visual
> Studio 2005 (Windows, obviously), and the C code works just fine, but
> when I try to use any C++ code, I get unresolved externals. I think I
> may have messed up the GMP compile at some point, so here are the
> steps I took to compile it:

<snip>

> After compiling GMP, I tried to use it within a new project. I added
> libgmp-3.lib and libgmpxx-3.lib to the linker input by going to
> "Project->Properties->Configuration Properties->Linker->Input" and
> adding them to the "Additional Dependencies" section. I compiled and
> executed a simple hello world app, and then copied libgmp-3.dll and
> libgmpxx-3.dll to the debug directory so they would be in the app
> path, and tried to compile the following program:
>
> #include <iostream>
> #include <gmpxx.h>
> using namespace std;
>
> int main (void)
> {
> 	mpz_class a, b, c;
>
> 	a = 1234;
> 	b = "-5678";
> 	c = a + b;
> 	cout << "sum is " << c << "\n";
> 	cout << "absolute value is " << abs(c) << "\n";
>
> 	return 0;
> }
>
> I received the following error:
>
> Error	13	error LNK2019: unresolved external symbol
> "__declspec(dllimport) class std::basic_ostream<char,struct
> std::char_traits<char> > & __cdecl operator<<(class
> std::basic_ostream<char,struct std::char_traits<char> > &,struct
> __mpz_struct const *)"
> (__imp_??6 at YAAAV?$basic_ostream at DU?$char_traits at D@std@@@std@@AAV01 at PBU__mpz_struct@@@Z)
> referenced in function "class std::basic_ostream<char,struct
> std::char_traits<char> > & __cdecl operator<<<struct __mpz_struct
> [1]>(class std::basic_ostream<char,struct std::char_traits<char> >
> &,class __gmp_expr<struct __mpz_struct [1],struct __mpz_struct [1]>
> const &)"
> (??$?6$$BY00U__mpz_struct@@@@YAAAV?$basic_ostream at DU?$char_traits at D@std@@@std@@AAV01 at ABV?$__gmp_expr@$$BY00U__mpz_struct@@$$BY00U1@@@@Z)	main.obj
>
> I tried removing using namespace std and instead using std::cout, but
> I received the exact same error. What's strange is that I can compile
> programs with gmp.h using the C commands only, and it works great -
> even with C++ commands, just not the C++ wrapper for gmp. If I have
> to, I can stick with C only commands, but the C++ wrapper would be
> really convenient. Any help would be appreciated - thanks!

Hello Jeremy,

linking C++ code compiled via gcc and the Microsoft toolchain is next to
impossible due to different name mangling conventions (feel free to
correct me if you know that I am wrong). In case of the C++ wrapper for
gmp there is a gmp port for Windows by Brian Gladman. Have a look at

 http://fp.gladman.plus.com/computing/gmp4win.htm

Hope this helps.

Cheers,

Michael