#include <libotr/proto.h>

int main(int argc, char const *argv[])
{
  OTRL_INIT;
  // OtrlUserState userstate = otrl_userstate_create();

  return 0;
}

g++ main.cpp -o main -L /usr/local/lib/ -lotr

Undefined symbols for architecture x86_64:
  "otrl_init(unsigned int, unsigned int, unsigned int)", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [bin/bin] Error 1

extern "C" {
  #include <libotr/proto.h>
}