Re: [Vala] Initializing strings to be used by FileStream::gets

[Jürg Billeter <j bitron ch>]

Hi Daniel,

On Sun, 2007-09-09 at 11:57 +0100, Daniel Thompson wrote:
> I am playing with vala and am starting out by playing with the string
> handling (always an interesting area when C and other languages meet).
>
> I used the following code to attempt to simulate 'cat' with no
> arguments.
>
> var str = new string();
> while (!stdin.eof()) {
>       stdin.gets(str, 256);
>       stdout.printf("%s", str);
> }
>
> Of course such code is broken because the string has only sufficient
> space allocated for the '\0' terminator meaning that fgets() will
> overrun the memory allocated for str (got this from review of the
> generated C code and proved it with valgrind).
>
> I've therefore been trying to figure out how best to grow a string to be
> large enough to store the input from fgets. The best I have so far
> developed without modifying the bindings is:
>
> var str = "%*d".printf(256, 0);
>
> This at least allows 256 to be a numeric constant somewhere and runs
> cleanly with valgrind but it really is pretty grubby.
>
> Have I missed something obvious? If not does anyone have any advice on
> how I should improve the bindings?

The string class in Vala should be treated as immutable in most cases,
just like the String classes in C# and Java. I'd recommend you to use
GLib.String (GString in C) if you want a string class that is better
suitable for modification. GLib.String can be compared to the
StringBuilder classes in C# and Java, maybe we should rename the class
in the Vala bindings to reduce some confusion about "string" and
"String".

Something like the following should work:

var str = new String.sized (256);
stdin.gets (str.str, 256);

What do other people think about renaming GLib.String to
GLib.StringBuilder?

Jürg