Hi Ross,
You don't say which version of Delphi you're using, but I assume it's
pre-Unicode support, since you use PChar instead of PAnsiChar or PWideChar.
Out of curiosity I built a small test application and traced through the
source code for this snippet of code using the CPU window. What I
noticed is that the address of the two strings assigned to 'a' and 'b'
are part of program memory. More specifically, Delphi appears to store
these strings immediately after the "return" opcode for the procedure
and simply puts those addresses into 'a' and 'b'. Since this area of
memory is protected while the application is running, that's why you get
the error.
By using:
a:=AllocMem(10);
StrCopy(a, 'abcdefghi');
b:='jklmnopqr';
StrCopy(a, b);
The variable 'b' now points to application memory while 'a' is allocated
a "write-enabled" memory address, so the access violation doesn't occur.
Regards,
Bevan
On 12/05/2013 5:30 p.m., Ross Levis wrote:
I did see a & b had a pointer address allocated. It looked like a
normal pointer address range. I'll try allocating 10 bytes to a later
and see what happens.
Ross.
*From:*[email protected]
[mailto:[email protected]] *On Behalf Of *Bevan Edwards
*Sent:* Sunday, 12 May 2013 4:48 PM
*To:* [email protected]
*Subject:* Re: [DUG] StrCopy problem
Actually, based on that article a:='abcdefghi' should assign 10 bytes
and include the zero byte at the end. But I wonder if the problem is
due to where this data is stored and trying to copy b to a results in
an attempt to write to protected memory?
Have you tried allocating 10 bytes of memory to 'a' and then using
StrCopy?
Have you run the debugger and checked where the PChars 'a' and 'b' are
pointing to before StrCopy?
-------- Original message --------
From: Ross Levis <[email protected]
<mailto:[email protected]>>
Date:
To: 'NZ Borland Developers Group - Delphi List'
<[email protected] <mailto:[email protected]>>
Subject: Re: [DUG] StrCopy problem
Doesn't really help.
a := 'abcdefghi' does allocate 9 bytes of RAM. I can access a and b
after it is assigned. The problem is StrCopy crashes. I would expect
"a" to have the same string as b once this is executed.
Ross.
*From:*[email protected]
<mailto:[email protected]>
[mailto:[email protected]] *On Behalf Of *Keith
Allpress
*Sent:* Sunday, 12 May 2013 10:27 AM
*To:* 'NZ Borland Developers Group - Delphi List'
*Subject:* Re: [DUG] StrCopy problem
Perhaps:
http://rvelthuis.de/articles/articles-pchars.html
*From:*[email protected]
<mailto:[email protected]>
[mailto:[email protected]] *On Behalf Of *Ross Levis
*Sent:* Sunday, 12 May 2013 2:39 a.m.
*To:* 'NZ Borland Developers Group - Delphi List'
*Subject:* [DUG] StrCopy problem
var
a: pChar;
b: pChar;
begin
a := 'abcdefghi';
b := 'jklmnopqr';
StrCopy(a,b);
end;
Question: Why does this code crash?
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