mutable string

[Jonathan M Davis via Digitalmars-d-learn]

On Sunday, July 10, 2016 23:38:26 ag0aep6g via Digitalmars-d-learn wrote:
> On 07/10/2016 11:26 PM, Adam Sansier wrote:
> > For example, I'm trying to compare a wchar buffer with a wstring using
> > slices:
> >
> > x[0..$] == y[0..$]
> >
> > It fails. I think because x has length 1024. If do
> >
> > x[0..y.length] == str[0..y.length]
> >
> > it fails, also because y has length 1024(since it was generated from a
> > buffer and the length wasn't set correctly).
>
> So you fill the buffer with a call to some Windows function. The Windows
> function either returns the amount of data it wrote, and/or it
> zero-terminates the string which it writes.
>
> If it returns the length, you use that when slicing the buffer. Then you
> can compare.
>
> If it zero-terminates, you search for zero in the buffer and count along
> to determine the length. I wanted to say that there's a function for
> this in phobos, but fromStringz [1] seems to be for char arrays only.
>
>
> [1] https://dlang.org/phobos/std_string.html#.fromStringz

There's std.utf.toUTFz for converting to arbitrary, null-terminated,
strings, but I don't think that there's a fromUTFz. fromStringz is a more
recent addition, I believe, and whoever added it, didn't add the more
general version.

However, there _is_ a function to get the length of a zero-terminated
wchar*/wchar[]. You can use core.stdc.wchar_.wcslen and pass it a pointer to
the buffer - e.g.

auto length = wcslen(buffer.ptr);

So, when you call the Windows function, you end up with something like

wchar[1024] buffer;
auto result = someWindowsFunc(buffer.ptr, someArg, someOtherArg);
if(/+ result is error +/)
    throw new Exception("some error message");
buffer[$ - 1] = '/0'; // just in case
wstring str = buffer[0 .. wcslen(buffer)].idup;

- Jonathan M Davis