Jezra.net: Vala musings : int to string, packages, and starting with main

Vala musings : int to string, packages, and starting with main

2008-11-03

Recently, I decided to start learning the Vala programming language. As with any programming language, I find that the easiest way to learn is to create a real world program, and I don't mean "hello world". During the start of my Vala development, I became aware of a few issues that took me a while to hunt down solutions for and I thought it would be best to share the info I have collected. Vala, as of this writing, is at version 0.4 and being quite new, the language doesn't have the most in-depth documentation, so I'll use working code examples.

Issue 1: How do I convert an integer into a string in Vala?
Answer: Vala strings are the same as GLib strings - Gstrings, yea, laugh it up. As such one can use the "printf" function of the string object to change an integer to a string. Take the following code as an example:

//nearly all vala apps will use Glib
using GLib;

//create a class that will we will call to print a string
public class Printer {
    //create a function that we can use to print a string
    public void print_line(string str)
    {
        stdout.printf("%sn",str);
    }
}

//create the main class
private class Main {
    //create the entrance to the application
    private static void main()
    {
        //make an instance of the printer
        var printer = new Printer();
        printer.print_line("hello world");
        //loop 5 times
        for(int i=0; i<5; i++)
        {
            // convert the integer value of i to a string
            string i_string = "%d".printf(i);
            //print the value of i
            printer.print_line("i = "+i_string);
        }    
    }
}

OK, did you copy the code and paste into your favorite editor?
Let's look at line 25:

string i_string = "%d".printf(i);

I created a string object named 'i_string' and set it equal to a string object that is print formatting an integer.

Issue #2: How do I list the actual name of the package that I can include when I'm compiling with valac?
Answer: When compile a Vala app that uses libraries like GTK, XML or Webkit, one needs to add '--pkg [packagename]' to the compile arguments used by valac. A list of the available packages can be found by doing the following:
1. on the commandline enter 'which valac' to find the install location of the valac compiler, since my compiler is installed in /usr/local/bin.....
2. on the commandline, I enter 'ls /usr/local/share/vala/vapi' and I will see a list of all of the packages I can use.
Had my valac been installed in /usr/bin, I would search for packages in /usr/share/vala/vapi

Issue #3: OK, this isn't really an issue, but it was a oddity that I had to accept. All Vala apps have an entry point in a function named "main", that is to say, that Vala code starts execution at a function named "main" and this function can create an instance of the class that "main" is a function of. To me this seemed very weird. Oh well, I got over it. Re-writing the above code to show the main function creating an instance of the class that main is a function of results in the following code:

//nearly all vala apps will use Glib
using GLib;
//create the printer class
private class Printer {
    //create a function that we can use to print a string
    public void print_line(string str)
    {
        stdout.printf("%sn",str);
    }
    //create the entrance to the application
    private static void main()
    {
        //make an instance of the printer
        var printer = new Printer();
        printer.print_line("hello world");
        //loop 5 times
        for(int i=0; i<5; i++)
        {
            // convert the integer value of i to a string
            string i_string = "%d".printf(i);
            //print the value of i
            printer.print_line("i = "+i_string);
        }    
    }
}

By the way, I've been happily writing all of my Vala code using valide: a Vala specific IDE.

Vala musings : int to string, packages, and starting with main from jezra.net

Comments

2008-11-11 jezra:

Oh geez. I could have used the "to_int()" method of the string class. Example:
string number="1";
int value = number.to_int();

2008-12-29 Justin:

I think you mean that you could have used to_string().

For example, instead of

string i_string = "%d".printf(i);

you could have written

string i_string = i.to_string();

Thank you very much for the post though. Vala has caught my interest.

Justin

2008-12-29 jezra:

oops,
Yes, I should/could have used 'to_string()' to convert the int to a string.
Thanks for the catch.

2009-08-18 Arkadi:

Thank you very much for your post.
I'm learning VALA too and writing a blog my self... Good luck.

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