string vs. w/char*

[Denis Koroskin]

On Mon, 28 Feb 2011 19:35:47 +0300, Tyro[a.c.edwards] <nospam at home.com>  
wrote:

> On 2/28/2011 11:08 PM, J Chapman wrote:
>> == Quote from Tyro[a.c.edwards] (nospam at home.com)'s article
>>> Both implementations results in error code 1812 being returned from
>>> GetLastError. explanation of the code reads:
>>>        ERROR_RESOURCE_DATA_NOT_FOUND
>>>        1812 (0x714)
>>>        The specified image file did not contain a resource section.
>>> The code I'm porting initially consisted of a resource.h file, a
>>> generic.rc file and two icons. I have not tried to include the icons  
>>> and
>>> generic.rc file in the compilation because I do not know how to as yet
>>> and I've only used half of the resource.h file: didn't think I need the
>>> whole thing. Could this be the reason for the error? If so could you
>>> direct me to the explanation of how to prepare these files for  
>>> inclusion
>>> in the compilation process?
>>> Thanks,
>>> Andrew
>>
>> You need to compile the .rc file (see
>> http://www.digitalmars.com/ctg/rcc.html), then add the resulting .res  
>> file
>> to dmd's command line.
>
> Awesome, this does the trick. However I get get a "GP Fault"? during  
> execution. Using windbg, I tracked it down to this piece of code:
>
> void Create()
> {
>    _hwnd = CreateWindowExA(
>      _exStyle,
>      cast(const(char*))_wc.GetName(), // returns string
>      cast(const(char*))_windowName,   // string variable
>      _style,
>      _x,
>      _y,
>      _width,
>      _height,
>      _hWndParent,
>      _hMenu,
>      _wc.GetInstance(),
>      _data);
>
>      assert(_hwnd, "Internal error: Window Creation Failed.");
> }
>
> The program craps at assert() but the error is generated. It just  
> displays a dialog box with the message: "test.exe has stopped working,  
> Windows is checking for a solution to the problem..."
>
> I'm thinking that _hwnd was never initialized and that assert is access  
> a null pointer but I cannot be sure. Any suggestions or ideas?

The

>  cast(const(char*))_wc.GetName()

line look *very* suspicious. You can't get a string and just cast it to  
const(char)*. Most importantly, the string (most likely) is not  
null-terminated.

What you need to do here is the following:

auto className = toStringz(_ws.GetName());
auto caption = toStringz(_windowName);

and pass those 2 to the function.

Alternatively, you could make sure your strings are null-terminated and  
pass the pointer directly (e.g. _windowName.ptr):

string _windowName = "foo"; // null-terminated automatically
string _caption = ("Hello, World" ~ "\0")[0..$-1]; // append trailing zero  
to an existing string but exclude it from result (so that it's not  
included in _caption.length)