Exception Safe Programming

[Tyler Knott]

Saaa wrote:
> Maybe I still don't get it :/
> 
> I made this simple function (mostly stolen :)
> 
> void getPictureList(char[] dir, out char[][] files){
>   isdir(dir);
>   files = std.file.listdir(dir, "*.png");
> 
>   foreach (d; files)
>   writefln(d);
>   writefln(files.length);
>   //if(files.length < 12) throw new Exception("Not enough images 
> found(<12)");
> }
> 
> When I uncomment the last line I get:
> Error: pictures: The system cannot find the file specified.
> (commented version doesn't generate any errors)
> 
> There are only 10 files so an exception should be trown, but not that one ! 
> : )

Somewhere in your program you're trying to open a file called "pictures" which 
is non-existent (at least where the system is looking) causing an exception.

> 
> I call the function in my main and at the end of my main there is:
> 
> scope(failure)
> {
>   writefln("Press the 'any' key to quit");
>   getchar();
> }
> 
> Why isn't this run in the uncommented version?

Scope guards are excecuted in the reverse order of where they're declared. 
E.g., using the thrower() function from my last example:

void main()
{
	scope(exit) { writefln(); } //newline
	scope(failure)
	{
		writef("scope guards."); //Note: writef (no ln) doesn't add '\n'
	}
	scope(failure)
	{
		writef("of ");
	}
	scope(failure)
	{
		writef("an example ");
	}
	thrower();
	scope failure(failure)
	{
		writef("This is ");
	}
}

This will print:

an example of scope guards.