From:	Erik Berglund <erik2 DOT berglund AT telia DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: ANY help would be greatly appreciated...
Lines:	73
Message-ID:	<yNTu4.988$y3.193543168@newsb.telia.net>
Date:	Tue, 29 Feb 2000 17:58:54 GMT
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Tim <opus AT wam DOT umd DOT edu> wrote: 
>
> Exiting due to signal SIGSEGV
> General Protection Fault at eip=00011d23
> eax=2074752f ebx=0003032c ecx=0003036c edx=00030364 esi=00000038
> edi=00000038
> ebp=01b86f10 esp=01b86f00 program=C:\BSO\ACCESS~1\CONVERT.EXE
> cs: sel=00a7  base=83405000  limit=01b86fff
> ds: sel=00af  base=83405000  limit=01b86fff
> es: sel=00af  base=83405000  limit=01b86fff
> fs: sel=0087  base=00008250  limit=0000ffff
> gs: sel=00bf  base=00000000  limit=0010ffff
> ss: sel=00af  base=83405000  limit=01b86fff
> App stack: [01b87000..01b07000]  Exceptn stack: [00029520..000275e0]
> 
> Call frame traceback EIPs:
>   0x00011d23
>   0x0001026c
>   0x0000e593
>   0x00001e47
>   0x000025fa
>   0x00011796
> 
> My code is here, the offending line it seems (or at least where the
> program dumps out with a seg fault is the line in the function
> stripBlanks() that I've isolated in <<<<<| xxxxx |>>>>>. I've
> iincluded the other code in case someone might actually bother to see
> if there is something else wrong. However, as I said before, my driver
> works perfectly in UNIX, but crashes in DOS/Windows. The driver is at
> the very bottom, along with the correct output followed by the
> incorrect output. Thanks in advance to anyone who cares to take the
> time to help me.
> 
> string& string::operator +(string& x) {
>  if(x.length!=0) {
>	int newlength = length + x.length;
>	char *tempstring = new char[newlength+1];  <--- 1.newlength
>	int counter, counter2;
>
>	for(counter=0; counter < length; counter++) {
>	     tempstring[counter] = data[counter];
>	}
>       tempstring[counter] = '\0';
>   cout << "This is from inside +: " << tempstring << endl;
>	for(counter2=0; counter2 < x.length; counter2++) {
>	     tempstring[counter + counter2] = x.data[counter2];
>	}
>	tempstring[counter + counter2] = '\0';  <--- 2.before cout
>   cout << "This is from inside +: " << tempstring << endl;
>	delete [] data;
>	length = newlength;
>	data = tempstring;
>  }
>  return *this;
> }

I think I've found the error.  It was in string operator,
see included text "<---".  The problem before was that
the new allocation at <---1. was too small and the routine
was writing past the end of the allocated buffer, and
that caused a SIGSEGV later in another new (which is
correct in itself).

<---2. is needed because otherwise the cout output will
be incorrect.

Hope this helps,

--
Erik Berglund
erik2 DOT berglund AT telia DOT com

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