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nrivera.eng@gmail.com
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 Posted: Mon Aug 01, 2005 6:05 pm Post subject: Puzzle |
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Gurus,
This is the problem:
The code below outputs bogus data when the either: *( iter->second )
is used and causes a segfault or *(tools[iter->first]) is used the
curious things is that the output of iter->first is perfect and when
the input is verified by:
for(int i = 0 ; inventory && !inventory.eof(); i++ )
{
Tool tempTool;
inventory >> tempTool;
tools.insert( Record::value_type( tempTool.getRecordNum(),
&tempTool ) );
cout << *(tools[tempTool.getRecordNum()]); // Input verification
}
The data seems to be correctly input into the Map data structure so
WHY THE BOGUS OUTPUT and the SEGFAULT?
Here is the Output portion:
for( Record::const_iterator iter = tools.begin(); iter !=
tools.end(); ++iter)
{
cout << *(tools[iter->first])<< endl;
}
were Record is:
typedef map < int, Tool *, less< int > > Record;
and Tools is a ( int, string, int, double ) object
the << operator has been overloaded and verified.
Thanks,
Noel
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Alf P. Steinbach
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| Posted: Tue Aug 02, 2005 12:02 am Post subject: Re: Puzzle |
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* [email]nrivera.eng (AT) gmail (DOT) com[/email]:
You've already got excellent answers in [comp.lang.c++], namely, don't store
pointers to local variables that go out of scope.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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Antoun Kanawati
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| Posted: Sat Aug 06, 2005 11:20 am Post subject: Re: Puzzle |
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[email]nrivera.eng (AT) gmail (DOT) com[/email] wrote:
| Quote: | Gurus,
This is the problem:
The code below outputs bogus data when the either: *( iter->second )
is used and causes a segfault or *(tools[iter->first]) is used the
curious things is that the output of iter->first is perfect and when
the input is verified by:
for(int i = 0 ; inventory && !inventory.eof(); i++ )
{
Tool tempTool;
|
Try:
Tool *tempTool = new tempTool;
| Quote: | inventory >> tempTool;
|
inventory >> *tempTool;
| Quote: |
tools.insert( Record::value_type( tempTool.getRecordNum(),
&tempTool ) );
|
tools.insert( Record::value_type( tempTool.getRecordNum(),
tempTool ) );
| Quote: | cout << *(tools[tempTool.getRecordNum()]); // Input verification
}
|
In your original formulation, you're keeping the address of objects
that cease to exist when you hit the last line of the loop body.
The 'first' part of the value_type, being an integer, is not affected
by the transient nature of the object; however, the second part is
a "Tool *", and all of your Tool*'s point to objects that have ceased
to exist.
The modifications suggested above will create heap-based objects that
will survive the lexical scope of their creation.
You will need to delete these objects at some point, of course.
| Quote: |
The data seems to be correctly input into the Map data structure so
WHY THE BOGUS OUTPUT and the SEGFAULT?
Here is the Output portion:
for( Record::const_iterator iter = tools.begin(); iter !=
tools.end(); ++iter)
{
cout << *(tools[iter->first])<< endl;
}
were Record is:
typedef map < int, Tool *, less< int > > Record;
and Tools is a ( int, string, int, double ) object
the << operator has been overloaded and verified.
-- |
A. Kanawati
[email]NO.antounk.SPAM (AT) comcast (DOT) net[/email]
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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