Unable to compile example program in C++ 11

[lutonelli]

I have to use HElib for my thesis, so I installed it and tried the examples from HElib/examples/tutorial, in order to start encoding some data. I installed HElib following the INSTALL.md document and ran the examples as said in examples/README.md. I'm able to build the examples, get their executables and run them.

Then I tried writing a little program and compile it, but I obtain some errors. If I just include the header of HElib the program compiles and runs correctly, as in:

#include <helib/helib.h>

using namespace std;
using namespace helib;

int main(int argc, char* argv[])
{

    cout << "hello world" << "\n";

    return 0;
}

But when I try to use some HElib classes the program does not compile with "undefined reference" errors. The code I'm trying to compile is simple and taken from the HElib examples:

#include <helib/helib.h>

using namespace std;
using namespace helib;

int main(int argc, char* argv[])
{

    Context context = ContextBuilder<CKKS>().m(16 * 1024).bits(119).precision(20).c(2).build();

    cout << "distance=" << "\n";

    return 0;
}

I'm trying compiling it with:

g++-11 encrypt_mnist.cpp -o encrypt_mnist -I/home/lulu/helib_install/helib_pack/include

and the error I get in this case is:

/usr/bin/ld: /tmp/cccLr3H1.o: in function `main':
encrypt_mnist.cpp:(.text+0x9e): undefined reference to `helib::ContextBuilder<helib::CKKS>::build() const'
/usr/bin/ld: /tmp/cccLr3H1.o: in function `NTL::ZZ::Deleter::apply(_ntl_gbigint_body*)':
encrypt_mnist.cpp:(.text._ZN3NTL2ZZ7Deleter5applyEP17_ntl_gbigint_body[_ZN3NTL2ZZ7Deleter5applyEP17_ntl_gbigint_body]+0x18): undefined reference to `_ntl_gfree(_ntl_gbigint_body*)'
collect2: error: ld returned 1 exit status

I tried also compiling it with

-I/home/lulu/helib_install/helib_pack/lib 
-L/home/lulu/helib_install/helib_pack/lib 
-L/home/lulu/helib_install/helib_pack/lib -lhelib 
-I/home/lulu/helib_install/helib_pack/lib -L/home/lulu/helib_install/helib_pack/lib -lhelib

but none of the above options seem to work. The first three for example give me a "no such file or directory" error with respect to helib.h. The latter instead produces a lot of errors like the one I posted above.

My knowledge of C++ is very low, but no one seems to be able to help me.

Thanks in advance for the help.

[lutonelli]

This problem found a solution in this Stack Overflow question.