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Hi Ross,<br>
<br>
That's interesting, because I would have thought that using
StrCopy(Title, '12345') in this situation would have resulted in the
same problem - the compiler must allocate the string differently in
this case ;-)<br>
<br>
Regards,<br>
<br>
Bevan<br>
<br>
<br>
<div class="moz-cite-prefix">On 13/05/2013 2:31 a.m., Ross Levis
wrote:<br>
</div>
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<div class="WordSection1">
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">In
the end I did this…<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">var
TitleStr: string=’The DLL Title’;<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">var
Title: pChar;<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">Title
:= @TitleStr[1];<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">I
could then use CopyStr elsewhere.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">Cheers.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"
lang="EN-US"> <a class="moz-txt-link-abbreviated" href="mailto:delphi-bounces@listserver.123.net.nz">delphi-bounces@listserver.123.net.nz</a>
[<a class="moz-txt-link-freetext" href="mailto:delphi-bounces@listserver.123.net.nz">mailto:delphi-bounces@listserver.123.net.nz</a>] <b>On
Behalf Of </b>Bevan Edwards<br>
<b>Sent:</b> Sunday, 12 May 2013 7:52 PM<br>
<b>To:</b> NZ Borland Developers Group - Delphi List<br>
<b>Subject:</b> Re: [DUG] StrCopy problem<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Ross,<br>
<br>
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.<br>
<br>
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.<br>
<br>
By using:<br>
a:=AllocMem(10);<br>
StrCopy(a, 'abcdefghi');<br>
b:='jklmnopqr';<br>
StrCopy(a, b);<br>
<br>
The variable 'b' now points to application memory while 'a' is
allocated a "write-enabled" memory address, so the access
violation doesn't occur.<br>
<br>
Regards,<br>
<br>
Bevan<br>
<br>
<br>
<o:p></o:p></p>
<div>
<p class="MsoNormal">On 12/05/2013 5:30 p.m., Ross Levis
wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">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.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D">Ross.</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif""
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif""
lang="EN-US"> <a moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">delphi-bounces@listserver.123.net.nz</a>
[<a moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">mailto:delphi-bounces@listserver.123.net.nz</a>]
<b>On Behalf Of </b>Bevan Edwards<br>
<b>Sent:</b> Sunday, 12 May 2013 4:48 PM<br>
<b>To:</b> <a moz-do-not-send="true"
href="mailto:delphi@listserver.123.net.nz">delphi@listserver.123.net.nz</a><br>
<b>Subject:</b> Re: [DUG] StrCopy problem</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"> <o:p></o:p></p>
<div>
<div>
<p class="MsoNormal">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?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Have you tried allocating 10 bytes of
memory to 'a' and then using StrCopy?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Have you run the debugger and checked
where the PChars 'a' and 'b' are pointing to before
StrCopy?<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
<br>
<br>
-------- Original message --------<br>
From: Ross Levis <<a moz-do-not-send="true"
href="mailto:ross@stationplaylist.com">ross@stationplaylist.com</a>>
<br>
Date: <br>
To: 'NZ Borland Developers Group - Delphi List' <<a
moz-do-not-send="true"
href="mailto:delphi@listserver.123.net.nz">delphi@listserver.123.net.nz</a>>
<br>
Subject: Re: [DUG] StrCopy problem <br>
<br>
<br>
<o:p></o:p></p>
<div>
<div>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">Doesn’t really help.</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">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.</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">Ross.</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#1F497D"
lang="EN-US">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:#1F497D"
lang="EN-US"> <a moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">delphi-bounces@listserver.123.net.nz</a>
[<a moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">mailto:delphi-bounces@listserver.123.net.nz</a>]
<b>On Behalf Of </b>Keith Allpress<br>
<b>Sent:</b> Sunday, 12 May 2013 10:27 AM<br>
<b>To:</b> 'NZ Borland Developers Group - Delphi
List'<br>
<b>Subject:</b> Re: [DUG] StrCopy problem</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">Perhaps:</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"><a moz-do-not-send="true"
href="http://rvelthuis.de/articles/articles-pchars.html">http://rvelthuis.de/articles/articles-pchars.html</a></span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<div>
<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span
style="color:#1F497D" lang="EN-US">From:</span></b><span
style="color:#1F497D" lang="EN-US"> <a
moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">delphi-bounces@listserver.123.net.nz</a>
[<a moz-do-not-send="true"
href="mailto:delphi-bounces@listserver.123.net.nz">mailto:delphi-bounces@listserver.123.net.nz</a>]
<b>On Behalf Of </b>Ross Levis<br>
<b>Sent:</b> Sunday, 12 May 2013 2:39 a.m.<br>
<b>To:</b> 'NZ Borland Developers Group - Delphi
List'<br>
<b>Subject:</b> [DUG] StrCopy problem</span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">var</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> a: pChar;</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> b: pChar;</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">begin</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> a := 'abcdefghi';</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> b := 'jklmnopqr';</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> StrCopy(a,b);</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">end;</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D">Question: Why does this code
crash?</span><o:p></o:p></p>
<p class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span
style="color:#1F497D"> </span><o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><br>
<br>
<br>
<o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
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