Can't link against static library with Mingw on Linux - c++

Question

I have installed the GMP library and try to cross-compile with mingw-w64-posix.
My Library is in /usr/local/lib.
My compile command looks like the following:
x86_64-w64-mingw32-g++-posix src/factorial.cpp -o bin/factorial.win.o -I/usr/local/include -L/usr/local/lib -lgmp -lgmpxx
It throws an undefined reference error:
(I can remove the whole block from -L...., same error. Seems like the library doesnt link for some reason)
/usr/bin/x86_64-w64-mingw32-ld: /tmp/ccxY03WS.o:factorial.cpp:(.text$_ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_S3_[_ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_S3_]+0x27): undefined reference to `__gmpz_mul'
/usr/bin/x86_64-w64-mingw32-ld: /tmp/ccxY03WS.o:factorial.cpp:(.text$_ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_l[_ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_l]+0x26): undefined reference to `__gmpz_mul_si'
/usr/bin/x86_64-w64-mingw32-ld: /tmp/ccxY03WS.o:factorial.cpp:(.text$_ZN10__gmp_exprIA1_12__mpz_structS1_E7init_siEl[_ZN10__gmp_exprIA1_12__mpz_structS1_E7init_siEl]+0x1a): undefined reference to `__gmpz_init_set_si'
/usr/bin/x86_64-w64-mingw32-ld: /tmp/ccxY03WS.o:factorial.cpp:(.text$_ZN10__gmp_exprIA1_12__mpz_structS1_EC1EOS2_[_ZN10__gmp_exprIA1_12__mpz_structS1_EC1EOS2_]+0x2e): undefined reference to `__gmpz_init'
/usr/bin/x86_64-w64-mingw32-ld: /tmp/ccxY03WS.o:factorial.cpp:(.text$_ZN10__gmp_exprIA1_12__mpz_structS1_ED1Ev[_ZN10__gmp_exprIA1_12__mpz_structS1_ED1Ev]+0x14): undefined reference to `__gmpz_clear'
collect2: error: ld returned 1 exit status
However if i change my compiler to g++ instead everything works fine.

Answer 1

OK -
The link errors (__gmpz_init, __gmpz_clear, etc.) are GMP "internals". They're supposed to come from libgmp, the C-language base library.
The code that's referencing them (.text$ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_S3[ZN23__gmp_binary_multiplies4evalEP12__mpz_structPKS0_S3], etc.) is "name mangled" C++.
I suspect the problem is that your "gmpxx" library was built with a different C++ compiler, that has a different "name mangling" convention than MinGW.
SOLUTION:
Download the complete libGMP source (e.g. from https://gmplib.org/, and rebuild EVERYTHING (including libgmpxx) with your libmingw-w64-posix++ C++ cross-compiler.
ADDENDUM:
I downloaded gmp-6.2.1 source, and found __gmpz_clear here:
gmp-6.2.1\gmp-h.in
#define mpz_clear __gmpz_clear
__GMP_DECLSPEC void mpz_clear (mpz_ptr);
"gmp-h.in" is a template used by the project's "autoconf", to generate the libGMP source files for the specified target environment.
Which, in turn, means:
The project you started out with (in your original question) wasn't configured for MinGW
... and ...
You didn't run "configure" correctly when you tried building from source.
SUGGESTION:
Try building libGMP from source again. DELETE everything, re-extract from the libGMP tarball, and carefully follow the INSTALL instructions:
./configure
make
make check <= VERY IMPORTANT!!
make install
I'm curious about your build environment (Windows? Linux?), compiler (exact MinGW version) and target (if you're building on a Windows workstation, do you want to run your GMP app as a Windows .exe)?