Hi,

I've got an immutable string declared in module scope, and I attempted to get a pointer to its characters through both &str[0] and str.ptr. However, it appears to me that the string is behaving like a manifest constant, in that the pointer is null.

The language reference indicates that it has a location in memory and thus has a pointer.

So, my question is thus: Is this a bug in DMD, or is this just something I missed?

Thanks

David

On 02/10/2018 11:26 PM, David Zhang wrote:
> I've got an immutable string declared in module scope, and I attempted to get a pointer to its characters through both &str[0] and str.ptr. However, it appears to me that the string is behaving like a manifest constant, in that the pointer is null.
> 
> The language reference indicates that it has a location in memory and thus has a pointer.
> 
> So, my question is thus: Is this a bug in DMD, or is this just something I missed?

The pointer should not be null, even when `str` is a manifest constant. But without code it's impossible to say if you're hitting a compiler bug or if you're doing something wrong.

On Saturday, 10 February 2018 at 22:36:41 UTC, ag0aep6g wrote:
> On 02/10/2018 11:26 PM, David Zhang wrote:
>> I've got an immutable string declared in module scope, and I attempted to get a pointer to its characters through both &str[0] and str.ptr. However, it appears to me that the string is behaving like a manifest constant, in that the pointer is null.
>> 
>> The language reference indicates that it has a location in memory and thus has a pointer.
>> 
>> So, my question is thus: Is this a bug in DMD, or is this just something I missed?
>
> The pointer should not be null, even when `str` is a manifest constant. But without code it's impossible to say if you're hitting a compiler bug or if you're doing something wrong.

Ah, yeah.

It appears to occur only when compiled in x86 mode.

This is what I'm talking about:

void createWindow( ... ) {

    assert( wndclassName.ptr ); //This fails

    HWND hwnd = CreateWindowW(
        wndclassName.ptr, //This too
        null,
        0,
        CW_USEDEFAULT, CW_USEDEFAULT,
        CW_USEDEFAULT, CW_USEDEFAULT,
        null,
        null,
        null,
        null
    );
}

wstring wndclassName = "wndclass_name"w;

Building with Visual Studio seems to be fine. This isn't an OptLink issue, is it?

On 02/10/2018 11:46 PM, David Zhang wrote:
> This is what I'm talking about:
> 
> void createWindow( ... ) {
> 
>      assert( wndclassName.ptr ); //This fails
> 
>      HWND hwnd = CreateWindowW(
>          wndclassName.ptr, //This too
>          null,
>          0,
>          CW_USEDEFAULT, CW_USEDEFAULT,
>          CW_USEDEFAULT, CW_USEDEFAULT,
>          null,
>          null,
>          null,
>          null
>      );
> }
> 
> wstring wndclassName = "wndclass_name"w;

That's not enough code to reproduce the issue. This works as far as I see:

----
import core.sys.windows.windef: HWND;
import core.sys.windows.winuser: CreateWindowW, CW_USEDEFAULT;

void main()
{
    assert( wndclassName.ptr );

    HWND hwnd = CreateWindowW(
        wndclassName.ptr,
        null,
        0,
        CW_USEDEFAULT, CW_USEDEFAULT,
        CW_USEDEFAULT, CW_USEDEFAULT,
        null,
        null,
        null,
        null
    );
}

wstring wndclassName = "wndclass_name"w;
----

But there is a recent regression on Windows that might be related. Do you also have a static constructor (`static this`) that uses `wndclassName`? If so, you might be hitting issue 18412.

https://issues.dlang.org/show_bug.cgi?id=18412

If you don't have a static constructor, it might be a different bug. In that case, please provide complete code so that we can get to the bottom of it.

On Saturday, 10 February 2018 at 22:59:18 UTC, ag0aep6g wrote:
> But there is a recent regression on Windows that might be related. Do you also have a static constructor (`static this`) that uses `wndclassName`? If so, you might be hitting issue 18412.
>
> https://issues.dlang.org/show_bug.cgi?id=18412
>
> If you don't have a static constructor, it might be a different bug. In that case, please provide complete code so that we can get to the bottom of it.

I have a static constructor that uses wndclassName to register the window class... at the top of the file.

I think that's the bug.