coding a commandLine class

**mickey** · 22nd November 2007, 01:19

Hello,
I'm coding a class that can parse the main() parameters; I follow example on Primer 3rd edition; it says to encapsulate the command line option (eg: "nameapplication.exe -f input.txt -t 45 - u 80") into CommandLine class; and write method that can access to it's members; in my case I have one field "string inputFile;". But I notice that, this implementation it much tied to the problem I'm solving(ie: this class seems me not much reusable, does it?).
Could anyone get me help? (I understood alright the book??)

thanks.

**wysota** · 22nd November 2007, 10:14

Aren't you trying to reinvent the wheel? There are classes to do that. There is even a Qt based class available that performs such a task somewhere in the net. You might also look for getopt_long() implementation on Windows (it's a POSIX function, so it might be unavailable on your system). Or you could just iterate over argv and handle the options. I'd suggest the last solution...

Qt Code:

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int main(int argc, char**argv){
  for(int i=1;i<argc;i++){
    if(!strcmp(argv[i], "-o")){
      fileToOpen = argv[++i];
      continue;
    }
    /* ... */
  }
  return 0;
}

int main(int argc, char**argv){
  for(int i=1;i<argc;i++){
    if(!strcmp(argv[i], "-o")){
      fileToOpen = argv[++i];
      continue;
    }
    /* ... */
  }
  return 0;
}

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**mickey** · 22nd November 2007, 12:04

Originally Posted by wysota

Aren't you trying to reinvent the wheel? There are classes to do that. There is even a Qt based class available that performs such a task somewhere in the net. You might also look for getopt_long() implementation on Windows (it's a POSIX function, so it might be unavailable on your system). Or you could just iterate over argv and handle the options. I'd suggest the last solution...

Qt Code:

Switch view

int main(int argc, char**argv){
  for(int i=1;i<argc;i++){
    if(!strcmp(argv[i], "-o")){
      fileToOpen = argv[++i];
      continue;
    }
    /* ... */
  }
  return 0;
}

int main(int argc, char**argv){
  for(int i=1;i<argc;i++){
    if(!strcmp(argv[i], "-o")){
      fileToOpen = argv[++i];
      continue;
    }
    /* ... */
  }
  return 0;
}

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Hello, I don't understand what you mean fully...I have to parse the parameters. They are few. I prefer code it on my own (exercise!) and I shuldn't fill the main() so I fiund Primer idea (that was mine too) but I notice what I said in post#1.
Anyway: I see your code; Primer uses for matching the "swiches" eg:

Qt Code:

Switch view

for(int i=1;i<argc;i++){
  char* pchar = argv[i];
  switch (pchar[0]) {
    case '-': 
       switch (pchar[1]) {
            case 'f': prepare for file read
            case 'o': prepare for............
            case 'd': prepare for.............
      };
};

for(int i=1;i<argc;i++){
  char* pchar = argv[i];
  switch (pchar[0]) {
    case '-': 
       switch (pchar[1]) {
            case 'f': prepare for file read
            case 'o': prepare for............
            case 'd': prepare for.............
      };
};

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What do you prefer? In my aboce example if much long to code but if I had many option (eg 10) I have to match 10 if in your way; I think the switch is much more strong in this case ( it has to do one only match instead of 10).
If I had to parse option like "-wwi", with switch this is boring and long......
What do you say??
thank you.

**wysota** · 22nd November 2007, 12:18

It depends if you only have short params or also long params. What you say suggests you also have long params so using strcmp() or std::string::operator== or QString::operator== seems a better choice. An alternative (which I use myself for a different task) is to compute a hash of the argument (using qHash() for example) and then go for switch(). But this might be an overkill if you have just a few arguments. Building a suffix trie of all possible choices is an option as well, but again might be considered an overkill, because you only do the parsing once.

**mickey** · 22nd November 2007, 19:35

Sorry bur referring my post #1, there's no be answer.....Anyone that have read Primer?
Again: is that class implementation much tied to the problem that I have to solve??

**jacek** · 25th November 2007, 23:31

Originally Posted by mickey

Again: is that class implementation much tied to the problem that I have to solve??

I think you should implement a generic command line parser. You should tell it what parameters are valid, whether they are optional or not and so on. Using this information such class should be able to parse the command line, detect errors and let you access the values of paramters that were set by the user and default values for the rest.