Extract some command line args before passing remainder to legacy code

Question

How can one write code so as to fill in the first ellipsis below, so that the legacy code can be given a reduced argument list?:

int main(int argc, char **argv)
         


        

Answer 1

The simplest way I can think of is to make a copy of the argument list, filtering out the arguments that the legacy object should not have.

Something like the following pseudo code:

new_argc = 0;
new_argv = new char*[argc];
for (each argument in argc)
{
    if (should the argument be copied)
        new_argv[new_argc++] = argv[current_argv_index];
}
new_argv[new_argc++] = nullptr;

// ...

LegacyObhect leg(new_argc, new_argv);

// ...

Answer 2

You can try something like this

int main(int argc, char **argv)
{
  std::vector<char*> legArgv;
  for(int i = 0; i < argc; ++i) {
      // extract 1 or more optional arguments
      if(isOptional(argv[i])) {
       // ...
      }
      else {
          legArgv.push_back(argv[i]);
      }
  }
  legArgv.push_back(nullptr); // terminate argument vector

  // forward remaining
  LegacyObject leg(legArgv.size(), &(legArgv[0])); 
}