CODEWITHSUNDEEP
c++
mll36
mll36

Reputation: 61

Pass (argc, argv) variables to a function as (argv, argc) inside main in C++

I am using a function from a library that calls for the (argc,argv) command line functions from the main program to be passed directly to it; however, I only want to pass some arguments to it with the rest being evaluated in the main code not function. Below is a sample of the main code with evaluating arguments.

int main(int argc,char** argv)
{
     // Evaluate arguments
if ( argc > 9 ) {
    PrintUsage();
    return 1;
}
G4String input;
G4String macro;
G4String physicslist;
for ( G4int i=1; i<argc; i=i+2 ) {
    if      ( G4String(argv[i]) == "-i" ) macro = argv[i+1];
    else if ( G4String(argv[i]) == "-l" ) physicslist = argv[i+1];
    else if ( G4String(argv[i]) == "-g" ) input = argv[i+1];
    else if //pass the rest of the arguments to function below
  G4MPImanager* g4MPI = new G4MPImanager(argc,argv);

Any other arguments not evaluated above I want to pass to the function from an outside library, which requires being called as shown.

Thanks!

Upvotes: 0

Views: 4790

Answers (3)

Loki Astari
Loki Astari

Reputation: 264381

Create a vector of strings.
Erase the arguments you don't want from the vector.
You can then create a char*[] from the vector very easily (at the size is trivial).

 int main(int argc, char* argv[])
 {
      std::vector<char*>  args(argv, argv+argc+1);  // +1 to catch the last NULL at argv[argc]

      for(auto loop = args.begin(); loop != args.end();)
      {
          if      (/*Your Test 1 */) { /*STUFF 1*/ loop = args.erase(loop);}
          else if (/*Your Test 2 */) { /*STUFF 2*/ loop = args.erase(loop);}
          else                       { ++loop; /* If you did not remove it increment loop*/ }
      }
      // args.size() -1 becuase we have the extra NULL as the last argument.
      //             and argv[arc] should be null
      // &args[0]    is the address of the first member.
      //             vector keeps its data in contiguous memory so will look like an array
      G4MPImanager* g4MPI = new G4MPImanager(args.size() - 1, &args[0]);
 }

Upvotes: 2

user4815162342
user4815162342

Reputation: 154886

argv is simply an array of char pointers terminated by a final NULL pointer. You can create your own using my_argv = new char *[number_of_items + 1], where number_of_items is the number of arguments you want to cherry-pick from "real" argv (or your own strings). Such array can be passed to G4MPIManager constructor instead of the actual argv received in main().

Additional notes:

  • Don't forget to terminate argv with a NULL pointer.

  • The first member of argv, argv[0], will be expected to hold the "program name" and as such will be either ignored or only used to prefix diagnostic messages. Simply reuse the argv[0] you get from main().

  • argc should be such that argv[argc] == NULL, i.e. the same as the number_of_items above. Given that the argv array must contain program name as first member, argc will never be 0.

Upvotes: 2

vim
vim

Reputation: 444

You just have to construct new pair of argc and argv for whatever your i is and then pass it to your function.

int newArgc = argc - i;
char** newArgv = &argv[i];
G4MPImanager* g4MPI = new G4MPImanager(newArgc, newArgv);

Upvotes: 0

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