How make C++ programs (command line -related)?

[HenriK]

Hello hello!

I was just wondering how is it possible to create C++ program that I can run from the command line like this:

MyCompiler Hello.program

MyCompiler is the name of my program (file extension is .bin, .exe etc.) & Hello.program is file to be handled. The execution would be similiar to code compiling using gcc or g++.

How can I implement this?

[hanst99]

Any C++ program can be run from the command line. For taking arguments, you either have to declare main like this:

int main(int argc /*number of arguments+1*/, char** argv/*array containing C strings that are the arguments
passed - argv[0] is the programs name and path*/)

So what are you actually asking?

[HenriK]

OK, now I'm beginning to understand why these arguments are as parameters in main() -function.

[S G H]

This might help you:

bool StringIsEqual(char* Str1, char* Str2) // Compare two strings and tell us if they are equal.
{
 if(strlen(Str1) != strlen(Str2))
   return false;
 for(int i = 0; i < strlen(Str2); i++)
   if(Str1[i] != Str2[i])
    return false;
 return true;
}
int main(int argc, char* argv[])
{
  if(argc <= 1)
     return 0;
  if(StringIsEqual(argv[1],"TheParameterYouWish"))
    { /* Operations to do e.g. -o... use sscanf_s for further use of parameters... */ }
  return 1;
}

Take care, StringIsEqual will not always tell the truth. It's just a sketch.

[Duthomhas]

...also, a variety of options already exist in the standard library to compare strings.

For messing with command-line arguments, using the std::string class is most convenient:

#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main( int argc, char** argv )
  {
  vector <string> args( argv + 1, argv + argc );

  // Now the args vector contains all the arguments to your program
  // (but not the name of the program.)

  cout << argv[ 0 ] << " has " << args.size() << " arguments.\n";

  for (size_t n = 0; n < args.size(); n++)
    cout << n << ": \"" << args[ n ] << "\"\n";

  return 0;
  }

Comparing whether or not something is equal is now just a lookup. There are many ways to do it.

If you just want to know whether a particular argument is listed in args, and where:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

#include <algorithm> #include <iostream> #include <string> #include <vector> using namespace std; int main( int argc, char** argv ) { vector <string> args( argv + 1, argv + argc ); cout << argv[ 0 ] << " has " << args.size() << " arguments.\n"; for (size_t n = 0; n < args.size(); n++) cout << n << ": \"" << args[ n ] << "\"\n"; // Find the magic "-hello" argument. size_t n = std::find( args.begin(), args.end(), "-hello" ) - args.begin(); if (n < args.size()) cout << "Argument number " << n << " told me to tell you \"Hello\".\n"; return 0; }

D:\prog\cc\foo> a a has 0 arguments. D:\prog\cc\foo> a one two three a has 3 arguments. 0: "one" 1: "two" 2: "three" D:\prog\cc\foo> a x y -hello world a has 4 arguments. 0: "x" 1: "y" 2: "-hello" 3: "world" Argument number 2 told me to tell you "Hello". D:\prog\cc\foo>

I also have an old post that works very similarly to allow the user to switch on a string:
http://www.cplusplus.com/forum/beginner/13528/#msg65188
The idea is similar and useful, especially as it examples how to prepare strings for case-insensitive comparison.


If you want to use C-strings, the <cstring> library has the very handy strcmp() function, which specifically compares strings:
http://www.cplusplus.com/reference/clibrary/cstring/strcmp/

If you don't want to #include that, you can use the C++ char_traits<> class to do the same thing:
http://www.cplusplus.com/reference/string/char_traits/
(scroll down to the "compare" and "length" methods).

Hope this helps.