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A minor thing, really, but I've just wasted several hours on this bug:
I've been working on convincing a Delphi program to call procedures in a
DLL. This is new to me, so I figure I'll do things wrong. Thus, when
things go wrong, I blame myself, sometimes, as I found, needlessly:
procedure SimLibLogon(pszDBName: PChar) external "EKDWS.DLL";
procedure DoStuff;
var
System : String;
begin
System := 'VADER';
SimLibLogon(PChar(System));
end;
and I get an access violation. The problem? Delphi is stricter about
types than C. So, with the prototype I wrote for the procedure, Delphi
decides that the string is a constant, and just calls it with a pointer to
wherever the program stores its string constants.
The DLL was written in C. It gets a character pointer which, logically,
ought to be constant, but isn't strictly so. It tries to modify it.
(Consensus here is that it's probably trying to upper-case the string.)
The string is in non-modifiable memory, so I get an error. I blame
myself, try to fix it, and run in circles for a couple of hours.
Solution?
System := Format('VADER', []);
Compiler has been fooled, and the string is now in modifiable memory.
Sigh.
--
...computer contrarian of the first order... / http://aperiodic.net/phil/
PGP: 026A27F2 print: D200 5BDB FC4B B24A 9248 9F7A 4322 2D22 026A 27F2
--- --
Symbol table full - fatal heap error; please go buy a RAM upgrade from
your local Apple dealer
-- Apple MPW C Compiler error message
---- --- --
Generated at 14:02 on 01 Jul 2004 by mariachi 0.52