cli int arguments printf || atoi

[pleaseRespond]

Hello all, just trying to understand how to do this simple function. All I want to do with this little program is to make a cli argument "-c" and have the program assign the integer that comes after it to a variable. It obviously doesn't need the loop for such a simple function, but this is just a test program for me to learn how to do this for future programs that probably will need it.

So:

//new.cpp
#include <iostream>
#include <stdio>

using namespace std;

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

  int c = 0;

  for (int i = 1; i < argc; ++i)
    if( argv[i] == "-c" )  scanf("%d", &c);

  cout << c << endl << argc << endl; //argc just to be sure that there are indeed 3 arguments
}

//Another try, with atoi.
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

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

  int c = 0;

  for (int i = 1; i < argc; ++i) 
    if( argv[i] == "-c" )  c = atoi(argv[i+1]);


  cout << c << endl << argc << endl;

  return 0;
}

./new -c 128
0
3

when I added the cout to the loop it ran 3 times and there are indeed 3 arguments in argc so I think there's probably only a couple things it could be...

1. It isn't picking up the -c it's invoked with for some reason or another.
2. I have no idea how scanf or atoi are supposed to be used (I have a feeling this is it...)

I've tried making main nothing but:

cout << argv[1] << endl;

and the output shows the -c it's being called with so I just don't get why the loop isn't working.

So I'd just like to get some opinions on the best way to have integers as cli arguments and what I'm doing wrong please.

[vlad from moscow]

This condition

if( argv[i] == "-c" )

will be never equal to true because the address of the first element of the sttring literal "-c" wll be allways unique.

You should use std::strncmp function in the condition

if ( std::strncmp( argv[i], "-c", 2 ) == 0 )

Also it is better to define a character array instead of the literal

const char parm[] = "-c";

Then the condition can be rewritten the following way

if ( std::strncmp( argv[i], parm, sizeof( parm ) - 1 ) == 0 )

[pleaseRespond]

Thank you very much, vlad from moscow.

I tried it again with scanf() and it seemed that the scanf() function was causing the program to hang, so I tried with atoi again and got it working correctly now thanks to you.

//Working with atoi tyvm
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

using namespace std;

int main(int argc, char* argv[])
{
  int c = 0;
  const char parm[] "-c";

  for(int i = 1; i < argc; ++i)
  {
    if ( strncmp( argv[i], parm, sizeof( parm ) - 1) == 0 )
    {
      c = atoi(argv[i + 1]);
      cout << c << endl;
    }
  }

  return 0;
}

[vlad from moscow]

Here

const char parm[] "-c";

the assignment operator = is omitted

[TheIdeasMan]

Just a trivial point from me.

scanf returns an int which is equal to the number of values read - you should always make use of that to test whether it worked as expected. I am not sure whether you knew that already.

Also, your code looks like C code in a C++ program, perhaps you could aim to do things the "C++ way". It took me awhile to get used to that, I am still learning more "C++ things".

Any way I hope this isn't annoyingly trivial, hopefully provided a little that is useful.