Comments on: CreateProcess Declaration

By: Christian Wimmer

Christian Wimmer — Thu, 12 Nov 2009 19:41:15 +0000

@Krystian
Yes, you can make things safe in this way but it also means you need to know how. By using the compiler programmers won’t make this error from the beginning because the compiler shows an error.

By: Javier Santo Domingo

Javier Santo Domingo — Thu, 12 Nov 2009 19:04:19 +0000

I vote for the “var” modificator, a pointer can be nil.

By: Krystian

Krystian — Thu, 12 Nov 2009 18:48:21 +0000

Simple way to make it safe is to use UniqueString:

const
cCmdLine: string = ‘notepad.exe’;
var
sCmdLine: string;
begin
sCmdLine := cCmdLine;
UniqueString(sCmdLine); // This line can be surrounded by {$IFDEF UNICODE}…{$ENDIF}, but not required
CreateProcess(nil, PChar(sCmdLine), …

By: Remko

Remko — Thu, 12 Nov 2009 11:18:39 +0000

Yes as long as the string has a reference count it’s safe. This would not be safe though:

const
cCmdLine: string = ‘notepad.exe’;

var
sCmdLine: string;

begin
sCmdLine := cCmdLine;
CreateProcess(nil, PChar(sCmdLine)

By: Stebi

Stebi — Thu, 12 Nov 2009 09:38:51 +0000

Is this safe?

var
CmdLine: string;
[...]
CreateProcess(”, PChar(CmdLine), …);

By: Remko

Remko — Thu, 12 Nov 2009 07:42:15 +0000

Well it’s just a thought to improve this part where existing code might produce an access violation. I didn’t have the idea to change many functions like this… That said: if you have concrete examples of functions where it is a problem we can always correct those specific ones.

Indeed the idea is to translate pointer type to var *unless* nil may be passed. I don’t know if this was originally done because it’s convenient or make the translations close to the delphi ones.

I didn’t think about dynamically loaded functions at all, so this is a useful comment. I am open for suggestions

By: Patrick van Logchem

Patrick van Logchem — Thu, 12 Nov 2009 07:31:28 +0000

Nice idea – but there are many more functions that are originally declared as having pointer argument(s), but are instead declared as having ‘var’ arguments in Jwa, which indeed prevents passing nil pointers (like GetModuleHandleEx).

Why exactly did you choose for ‘var’ arguments in the first place? Because the Delphi RTL does the same? And why is that exactly?
And how are we supposed to call those methods when all we have is a pointer? Passing ({var}aPointer^) seems rather messy… especially when the pointer could be a nil value!

And in this situation, how should we retrieve the address of one specific overloaded function?

Also, are you planning to overload all API’s that have the same possible problem? (That is, given we can determine which ones they are.)