I would like to make a effective coding of this problem
function ADOConnectionWillExecute( Connection: TADOConnection; var CommandText:
WideString;
var CursorType: TCursorType; var LockType: TADOLockType;
var CommandType: TCommandType; var ExecuteOptions: TExecuteOptions;
var EventStatus: TEventStatus; const Command: _Command;
const Recordset: _Recordset) : TStringlist ;
begin
result.AddStrings(
CommandText,
'Before '+GetEnumName(TypeInfo(TCommandType),Integer(CommandType)),
GetEnumName(TypeInfo(TEventStatus),Integer(EventStatus)),
GetEnumName(TypeInfo(TCursorType),Integer(CursorType)),
GetEnumName(TypeInfo(TADOLockType),Integer(LockType)), 0);
end;
In the original code source from the internet all data are written into a GUI element, accepting strings and integer values, see Build your own profiler using ADO
.
My result.addstring does not work, wont do any type conversions to eg. default string and also use result.add(...) statement
What will be the most effective way to handle this data without much extra coding?
This is Delphi 101. You have to create an instance of a class before you can use it, and your code doesn't do so.
You need to create Result before you can access it.
Result := TStringList.Create;
Result.AddStrings(....);
When returning an object instance from a function, you need to keep in mind that it is the responsibility of the calling code to free it afterward, so make sure you protect that code with try..finally to make sure that happens to avoid memory leaks.
Saying "does not work" is totally meaningless, unless you explain what "does not work" means. Please remember when asking questions here that we can't see your screen or read your mind, so you need to be specific when you write your questions. If you say "does not work", explain what you mean by that phrase. If you say "I get an error", describe the error and provide the exact error message (if any) you're getting, including any memory addresses or error codes. You have that information right in front of you, clearly, or you wouldn't know things weren't working or that you were getting an error. There's absolutely no reason to not provide those details in your question.
Related
To allow multiselection in a file-open-dialog and to avoid this long expression:
OpenDialogSourceFiles.Options := OpenDialogSourceFiles.Options + [Vcl.Dialogs.fdoAllowMultiSelect]; // works
I tried to use the shorter Include function:
System.Include(OpenDialogSourceFiles.Options, Vcl.Dialogs.fdoAllowMultiSelect); // error
However, the compiler marks this as erroneous.
This is by design. The Include procedure requires a variable as its first argument (it is a var parameter, essentially, even though the procedure is implemented by compiler magic), but TFileOpenDialog.Options is a property.
Hence you must use the verbose alternative. There's nothing you can do about it.
The same thing applies to Inc and TComponent.Tag, for instance.
(But you can write fdoAllowMultiSelect instead of Vcl.Dialogs.fdoAllowMultiSelect, Include instead of System.Include, etc. to make it a bit less verbose.)
I have to access several functions of a DLL written in c from Delphi (currently Delphi7).
I can do it without problems when the parameters are scalar
(thanks to the examples found in this great site!), but I have been stuck for some time when in the parameters there is a pointer to an array of Longs.
This is the definition in the header file of one of the functions:
BOOL __stdcall BdcValida (HANDLE h, LPLONG opcl);
(opcl is an array of longs)
And this is a portion of my Delphi code:
type
TListaOpciones= array of LongInt; //I tried with static array too!
Popcion = ^LongInt; //tried with integer, Cardinal, word...
var
dllFunction: function(h:tHandle; opciones:Popcion):boolean;stdcall;
arrayOPciones:TListaOpciones;
resultado:boolean;
begin
.....
I give values to aHandle and array arrayOPciones
.....
resultado:=dllFunction(aHandle, #arrayopciones[0]);
end;
The error message when executing it is:
"Project xxx raised too many consecutive exceptions: access violation
at 0x000 .."
What is the equivalent in Delhpi for LPLONG? Or am I calling the function in an incorrect way?
Thank you!
LONG maps to Longint, and LPLONG maps to ^Longint. So, you have translated that type correctly.
You have translated BOOL incorrectly though. It should be BOOL or LongBool in Delphi. You can use either, the former is an alias for the latter.
Your error lies in code or detail we can't see. Perhaps you didn't allocate an array. Perhaps the array is incorrectly sized. Perhaps the handle is not valid. Perhaps earlier calls to the DLL failed to check for errors.
I have a TEmbeddedWB (https://sourceforge.net/projects/embeddedwb/) with an iFrame in it. I have to find out that a specific HTML Tag is inside that iFrame or not. My iFrame object is a IHTMLFrameBase2, while the Tag is a IHTMLElement. I know that the iFrame.contentWindow.document (which is a IHTMLDocument2) is the same as Tag.document. But the Tag.document is an IDispatch object, therefore the following gives a false:
if iFrame.contentWindow.document = Tag.document then ShowMessage('In iFrame')
else ShowMessage('Not in iFrame');
I know that the two object is the same, because the Watch List can show their memory address:
But I can't get their addresses from code. What I've tried:
Addr(iFrame.contentWindow.document) // Gives variable required error
#iFrame.contentWindow.document // Gives variable required error
Pointer(iFrame.contentWindow.document) //Compiles, but gives wrong address
Format('%p',[iFrame.contentWindow.document]) //Compiles, but gives EConvertError
Note: If I run line-by-line the addresses that the Watch List is showing change after EVERY line of code, no matter the code affects the WebBrowser or not.
From the rules of COM:
It is required that any call to QueryInterface on any interface for a given object instance for the specific interface IUnknown must always return the same physical pointer value. This enables calling QueryInterface(IID_IUnknown, ...) on any two interfaces and comparing the results to determine whether they point to the same instance of an object (the same COM object identity).
So, ask them both for their IUnknown interface, and compare.
var
disp: IDispatch;
doc: IHTMLDocument2;
....
if (disp as IUnknown) = (doc as IUnknown) then
....
I've got some code that worked fine under Delphi 2007 but breaks under D2010. It involves passing in a string, converting it to a PWideChar (specifically, a WideString pointer, not a UnicodeString pointer), doing some processing, and then calling SysFreeString on it. It works fine until a blank string is passed in, then SysFreeString breaks. It calls a bunch of things that end up raising an Int 3 breakpoint inside NTDLL.DLL. Continuing past this point results in
Project raised exception class
$C0000005 with message 'access
violation at 0x7747206e: read of
address 0x539b8dba'.
Which, if you look closely, is not the standard Access Violation message.
The top of the stack trace when it hits the Int 3 looks like this:
:774e475d ; ntdll.dll
:774afad0 ; ntdll.dll
:774e5de9 ; ntdll.dll
:774a6dff ; ntdll.dll
:76fc1075 ; C:\Windows\system32\ole32.dll
:770e443a ; C:\Windows\system32\oleaut32.dll
:770e3ea3 oleaut32.SysFreeString + 0x4a
Does anyone have any idea what's going on here?
Edit (from the comments):
This isn't a WideString, though. It's
a PWideChar generated by
StringToOleStr, and there are no
double-free errors when a non-blank
string is passed in. Unfortunately, I
can't really post a code sample
because this is a third-party
component that's under copyright. (And
I can't ask them for support because
it's no longer supported. Basically,
the whole thing's one big mess.)
I'm going to try psychic debugging. You've got some kind of heap corruption in your application and SysFreeString is the unfortunate victim (it's hard to tell without OS symbols, you should probably install the MSFT symbol packages for your OS).
Try enabling application verifier (in particular pageheap) for your app and see if it crashes earlier.
It is hard to diagnose without seeing your actual code, however WideString automatically calls SysFreeString() when it goes out of scope. It sounds like your code may be making a second call to SysFreeString() on memory that has already been freed. WideString itself has not changed at all between D2007 and D2010, but other aspects of Delphi's string handling have. Maybe you are not managing the strings correctly. Can you please show your actual code?
A simple test shows that you need to be really careful on what you do in which order.
So: even though you cannot post a small example, can you indicate what you are doing in a bit more detail?
Bad debugging; ignore the things below; see comment.
The SysFreeString() is being called at the end of the the Allocate() call, even though it returns a PWideChar:
program ShowStringToOleStrBehaviourProject;
{$APPTYPE CONSOLE}
uses
SysUtils;
function Allocate(const Value: UnicodeString): PWideChar;
begin
Result := StringToOleStr(Value);
// implicit SysFreeString(WideChars);
end;
procedure Run;
var
WideChars: PWideChar;
begin
WideChars := Allocate('Foo');
Writeln(WideChars);
end;
begin
try
Run();
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
Note the console still outputs 'Foo' because the memory has not been overwritten yet.
--jeroen
It can be different reasons of such kind of errors:
You try to free with SysFreeString a memory which are allocated not with SysAllocString, but for example with CoTaskMemAlloc.
You have heap correct.
Heap corruptions are difficult to localize. The function HeapSetInformation can be very helpful. For example you can use
HeapSetInformation(NULL,HeapEnableTerminationOnCorruption,NULL,0);
Other good way is usage of HeapValidate function. For example you can define a function which verify all heaps pf the process (code in C, which can be easy rewritten in Delphi):
BOOL MyHeapValidate (void)
{
HANDLE hProcessHeaps[1024];
DWORD i;
DWORD dwNumberOfHeaps;
BOOL bSuccess = FALSE;
dwNumberOfHeaps = GetProcessHeaps (sizeof(hProcessHeaps)/sizeof(hProcessHeaps[0]),
hProcessHeaps);
if (dwNumberOfHeaps > sizeof(hProcessHeaps)/sizeof(hProcessHeaps[0])) {
MessageBox(NULL, TEXT("GetProcessHeaps()"),
TEXT("Error in MyHeapValidate()"), MB_OK);
return FALSE;
}
for (i=0; i<dwNumberOfHeaps; i++) {
bSuccess = HeapValidate (hProcessHeaps[i], 0, NULL);
if (!bSuccess)
return bSuccess;
}
return bSuccess;
}
The usage of this function can be like following:
void BadFunction(BSTR bstr)
{
LPOLESTR psz = OLESTR("Test12");
lstrcpy (bstr, psz);
}
int main()
{
LPOLESTR psz = OLESTR("Test");
BSTR bstr = SysAllocString (psz);
// verify that before call of BadFunction() all process heaps are OK!
if (!MyHeapValidate()) {
_tprintf(TEXT("heap is corrupted after the step 1.\n"));
return 1;
}
BadFunction(bstr);
if (!MyHeapValidate()) {
_tprintf(TEXT("heap is corrupted after the step 1.\n"));
return 1;
}
SysFreeString (bstr);
return 0;
}
With respect of inserting MyHeapValidate() in different suspected places you can very quickly local the place of corruption.
+1 for Larry Osterman's answer.
Some Windows memory functions behave slightly different under debugger: if they detect some kind of misuse - they trigger breakpoint to notify debugger. So, basically, your code is doing something wrong.
You can install hooks on SysAllocString/SysFreeString and redirect them to your memory manager (which should be in full debug mode) to collect more info. Or you can just pass these calls through to original functions, installing only a filter, which watches for memory actions.
And you can install debug symbols to get more info too (I'm not sure if Delphi debugger can use it, but Process Explorer - can. You can connect it to your process and see call stack).
I tried to make my code as simple as possible,but I failed at it.
This is my code:
class function TWS.WinsockSend(s:integer;buffer:pointer;size:word):boolean;
begin
dwError := Send(s,buffer,size,0);
// Debug
if(dwError = SOCKET_ERROR) then
begin
dwError := WSAGetLastError;
CloseSocket(s);
WSACleanup;
case (dwerror) of
//Case statement
else
LogToFile('Unhandled error: ' + IntToStr(dwError) + ' generated by WSASend');
end;
Exit(false);
end;
// if the size of the bytes sent isn't the expected one.
while(dwError <> size) do
dwError:= dwError + Send(s,Ptr(cardinal(buffer) + dwError),size-dwError,0);
Exit(true);
end;
The error is placed at
dwError:= dwError + Send(s,Ptr(cardinal(buffer) + dwError),size-dwError,0);
Error is "Constant object cannot be passed as var parameter"
I understand I need a variable,but isn't there a way I can do it without adding one more line?
When the compiler complains about the way you're passing a parameter, the first thing you need to know is what the parameter expects. Therefore, you should go look at the declaration of Send. If looking at the declaration doesn't immediately give you an idea of what to fix, then you need to include that declaration with the code you post in your question.
I suspect that this actually has nothing to do with incrementing a pointer. Instead, the compiler is complaining about the third parameter, where you are trying to pass the expression size-dwError. I guess the parameter is declared like this:
var buffersize: Word;
The function plans on providing a new value for that parameter — that's what var means — so the thing you pass to that parameter needs to be something that can receive a value. You can't assign a new value to the result of subtracting two variables.
Take a closer look at where the compiler complained about that line. Didn't it place the cursor somewhere near the third parameter? That's a clue that the problem is there.
Decrement size, and then pass it to the function.
Dec(size, dwError);
Inc(dwError, Send(s, Ptr(cardinal(buffer) + dwError), size, 0));
Why do you care about adding another line? Have you reached your quota for the day? Lines are cheap; don't be afraid to use two to express yourself when one won't do. Likewise for variables. When your code doesn't work, saving a byte or two doesn't matter at all.
At the very least, you should have added more lines in order to track down the source of the problem. When you have one line of code that's performing several independent calculations (such as getting a new pointer value, getting a new size, and calling a function), break the line into several separate pieces. That way, if there's a problem with one of them and the compiler complains, you'll know exactly which one to blame.
Correct, this will not work as written. When your dealing with var parameters, you have to build the parameter BEFORE passing it to the procedure/function. When a Var parameter is passed, the procedure is allowed to modify it. If you attempted to copy two variables together on the call, where would this result go?
The other issue is that dwError is not delcared. A class method does NOT have access to the data elements of the object the class defines. If you drop the class, then you will have access to the data elements, but will require that the class first be created.
You should only be using class methods in places where the input and output are completely contained within the method.
How are you allocating your buffer? Internally is it an array?
Sounds like Send has a format parameter (like send (const something;size:integer)
Workaround is using pchar (entirepointerexpression)[0]