Re: Why could not display the string?
"Lee Tow" <fbjlt@pub3.fz.fj.cn> schrieb im Newsbeitrag
news:OlEeWa9sHHA.508@TK2MSFTNGP02.phx.gbl...
Hello all:
First I create a component using atl,look:
STDMETHODIMP CTpsz::PrtStr(wchar_t **str)
What does ypur IDL file look like. To return a wide character string using
wchar_t** it should be something like
HRESULT PtrStr([out, string] wchar_t** str);
But it would be much better to use BSTR* instead of wchar_t**.
{
// TODO: Add your implementation code here
ULONG cb=60;
wchar_t *tmp;
tmp=(wchar_t*)CoTaskMemAlloc(cb);
tmp=L"Hello World!";
str=&tmp;
What the h... are you doing here? First you allocate some memory and make
temp point to it. Then you overwrite that pointer making it point to some
static array of wchar_t's. Noone can free the memory allocated with
CoTaskMemAlloc now. And finally you assign the address of a local variable
(tmp) to another local variable (str). How should that be known to the
caller. For [out] parameters you are passing a pointer to some variable, to
be able to modify whatever this pointer points to (a wchar_t* inyour case),
not to modify the pointer itself, which only is a local variable in your
function.
Perhaps you should first try to make a simple C or C++ function that returns
some string, without worrying about COM/ATL first. Once you know exactly how
parameter passing in C and C++ work, you can apply that knowledge to
COM/ATL.
Heinz
return S_OK;
}
....