[Accessibility] [Accessibility-ia2] Newbie question: help withBSTR arrays
Rob Gallo
rgallo at FreedomScientific.com
Wed Feb 24 07:31:24 PST 2010
Brian,
On the client side, you need more error checking. You don't check the value
of res after some calls. And you don't check to make sure the returned out
parameters are valid. Any one of these things can go wrong. And you never
know what you'll get back from someone else's code.
Likewise, on the server side, you don't check the input parameters to make
sure they're non-null. And you don't check to make sure that the user hasn't
requested fewer key bindings than you provide.
There is at least one case when you don't initialize a local variable, which
you should always do, even when you're passing that variable to a function
using it as an out parameter. That allows you to be more confident in
correct checking of the return value of the parameter.
Also, if I were doing this, I would not free the BSTR's in the Process
function. It's easy to lose track of allocating and freeing memory. So, I
would have Process take a const wchar_t*, and have the function that
requested the actions free each BSTR in turn. That way, you can clearly see
where the memory was allocated (in the call to get the actions) and where it
is freed. This will give less responsibility to the Process function, and
make the memory allocation and deallocation easier for the next person to
understand.
Thanks,
RG
_____
From: accessibility-ia2-bounces at lists.linuxfoundation.org
[mailto:accessibility-ia2-bounces at lists.linuxfoundation.org] On Behalf Of
Pete Brunet
Sent: Tuesday, February 23, 2010 6:43 PM
Cc: accessibility at lists.linux-foundation.org; IA2 List
Subject: Re: [Accessibility-ia2] [Accessibility] Newbie question: help
withBSTR arrays
Hi Brian, I suspect there are some important readers that don't watch this
list. I'm cc'ing it to the IA2 list. -Pete
Brian Cragun wrote:
Thanks for your interest and patience. The following code seems to be
working. It shows a CLIENT fragment that calls for the key bindings and
then pulls them off for processing. The SERVER snippet shows how I am
building a simple three element BSTR array. Please advise if you see any
stupid errors being made.
Thanks!
Brian
CLIENT:
res =
m_spAccessible2->QueryInterface(IID_IAccessibleAction,(void**)&m_spAccessibl
eAction);
long nActions = 0L;
res = m_spAccessibleAction->nActions(&nActions);
if(SUCCEEDED(res)){
BSTR name;
BSTR description;
for (int iAction=0 ; iAction<nActions;
iAction++){
res =
m_spAccessibleAction->get_name(iAction, &name);
if(SUCCEEDED(res)){
Process(name); // Process
the name and free the string
}
res =
m_spAccessibleAction->get_description(iAction, &description);
if(SUCCEEDED(res)){
Process(description); //
Process the name and free the string
}
BSTR *aKeyBindings;
long aNumMaxBinding = 10;
long aNumBindings;
res =
m_spAccessibleAction->get_keyBinding(iAction, aNumMaxBinding, &aKeyBindings,
&aNumBindings);
if(SUCCEEDED(res)){
for (int jBind=0;
jBind<aNumBindings; jBind++){
Process(aKeyBindings[jBind]); // Process the name and free the string
}
CoTaskMemFree(aKeyBindings);
}
}
}
SERVER:
STDMETHODIMP AccServer::get_keyBinding(long aActionIndex, long
aNumMaxBinding,
BSTR **aKeyBinding,
long *aNumBinding)
{
*aKeyBinding = static_cast<BSTR*>(CoTaskMemAlloc((aNumMaxBinding) *
sizeof(BSTR*)));
if (!*aKeyBinding) return E_OUTOFMEMORY;
*aKeyBinding[0] = ::SysAllocString(OLESTR("0 key binding"));
// if (!*(aKeyBinding[0])) return E_OUTOFMEMORY;
(*aKeyBinding)[1] = ::SysAllocString(OLESTR("1 key
binding"));
// if (!*(aKeyBinding[1])) return E_OUTOFMEMORY;
(*aKeyBinding)[2] = ::SysAllocString(OLESTR("2 key
binding"));
// if (!*(aKeyBinding[2])) return E_OUTOFMEMORY;
*aNumBinding = 3L;
return S_OK;
}
Brian Cragun
IBM AbilityLab Consultant
Human Ability & Accessibility Center
<http://www.ibm.com/able> www.ibm.com/able & <http://w3.ibm.com/able>
w3.ibm.com/able
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From: Brian Cragun/Rochester/IBM at IBMUS
To: accessibility at lists.linux-foundation.org
Date: 02/22/2010 01:52 PM
Subject: [Accessibility] Newbie question: help with BSTR arrays
Sent by: accessibility-bounces at lists.linux-foundation.org
_____
I'm struggling to understand how a BSTR array is properly allocated and
content is added to it. Also how the BSTRs in the array are retrieved.
Does anyone have any simple examples?
The information at
<http://accessibility.freestandards.org/a11yspecs/ia2/docs/html/_generalinfo
.html#_arrayConsideration>
http://accessibility.freestandards.org/a11yspecs/ia2/docs/html/_generalinfo.
html#_arrayConsideration is useful but not quite enough for me.
I assume I need to allocation the memory with CoTaskMemAlloc and release it
with CoTaskMemFree.
Thanks!
- Brian
Brian Cragun
IBM AbilityLab Consultant
Human Ability & Accessibility Center
<http://www.ibm.com/able> www.ibm.com/able & <http://w3.ibm.com/able>
w3.ibm.com/able
W:(720)-663-2801 H:(507)288-2437
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_____
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--
Pete Brunet
a11ysoft - Accessibility Architecture and Development
(512) 238-6967 (work), (512) 689-4155 (cell)
Skype: pete.brunet
IM: ptbrunet (AOL, Google), ptbrunet at live.com (MSN)
http://www.a11ysoft.com/about/
Ionosphere: WS4G
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