Open File Dialog Box

I'm learning Objective-C and trying to develop a simple zipper application, but I stopped when now, when I need to insert a button at my dialog and this button opens a Ope开发者_StackOverflow中文版n File Dialog that will select a file to compress, but I never used a Open File Dialog, then how I can open it and store the user selected file in a char*? Thanks.

Remember that I'm using GNUstep(Linux).

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Thanks @Vlad the Impala I am updating your answers for people who use OS X v10.6+

// Create the File Open Dialog class.
NSOpenPanel* openDlg = [NSOpenPanel openPanel];

// Enable the selection of files in the dialog.
[openDlg setCanChooseFiles:YES];

// Multiple files not allowed
[openDlg setAllowsMultipleSelection:NO];

// Can't select a directory
[openDlg setCanChooseDirectories:NO];

// Display the dialog. If the OK button was pressed,
// process the files.
if ( [openDlg runModal] == NSOKButton )
{
    // Get an array containing the full filenames of all
    // files and directories selected.
    NSArray* urls = [openDlg URLs];

    // Loop through all the files and process them.
    for(int i = 0; i < [urls count]; i++ )
    {
        NSString* url = [urls objectAtIndex:i];
        NSLog(@"Url: %@", url);
    }
}

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In case someone else needs this answer, here it is:

 int i;
  // Create the File Open Dialog class.
  NSOpenPanel* openDlg = [NSOpenPanel openPanel];

  // Enable the selection of files in the dialog.
  [openDlg setCanChooseFiles:YES];

  // Multiple files not allowed
  [openDlg setAllowsMultipleSelection:NO];

  // Can't select a directory
  [openDlg setCanChooseDirectories:NO];

  // Display the dialog. If the OK button was pressed,
  // process the files.
  if ( [openDlg runModalForDirectory:nil file:nil] == NSOKButton )
  {
   // Get an array containing the full filenames of all
   // files and directories selected.
   NSArray* files = [openDlg filenames];

   // Loop through all the files and process them.
   for( i = 0; i < [files count]; i++ )
   {
   NSString* fileName = [files objectAtIndex:i];
   }

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For people who use OS X v10.10+, replace in Far Jangtrakool answer:

if ( [openDlg runModal] == NSOKButton )

by

if ( [openDlg runModal] == NSModalResponseOK )