An error when building

[xin li]

The link reported an error while building：

/usr/bin/ld: entry.o: in function void __gnu_cxx::new_allocator<cryptofuzz::module::OpenSSL>::construct<cryptofuzz::module::OpenSSL>(cryptofuzz::module::OpenSSL*)': /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/ext/new_allocator.h:146: undefined reference to cryptofuzz::module::OpenSSL::OpenSSL()'
/usr/bin/ld: entry.o:(.data+0x10f48): undefined reference to `typeinfo for cryptofuzz::module::OpenSSL'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Makefile:34: cryptofuzz] Error 1

Does anyone know why this error occurred🥲🥲🥲