Drew Vogel wrote:
> Warren Young wrote:
>
>> Drew Vogel wrote:
>>
>>> If I
>>> select all of the columns in the table (named, not using *), the
>>> last column (wpc_bludgeoning) is corrupted. When I select just the
>>> four wpc_* columns, the data in the third column (wpc_chopping)
>>> corrupted. In both scenerios, it corrupts the data in the last or
>>> third rows, respectively, for both rows in the result set.
>>
>>
>> Sounds like you have a memory bug somewhere. While it's possible
>> that it is in MySQL++, you'd think that someone else would have run
>> into something this blatant before.
>>
>> If you're running on a Linux or OS X machine, try running your
>> program under valgrind. If on Windows, you may only have the choice
>> of commercial programs like Bounds Checker.
>>
>
> I'm not sure I actually solved this, but it went away. I went over the
> execution path once more today (think fresh eyes might catch something
> new). I realized that the Connection object was never closed or
> deleted. I added a call to ->close() and a delete statement. Now the
> data corruption is gone.
>
> I am using the State Threads library, but the library never actually
> creates a new thread (the exception was being thrown in the startup
> code, before new threads are needed) so it is unlikely that this was
> causing a problem. Any ideas how closing or not closing the Connection
> object (well after the conversion is made) could have any effect on
> the conversion? If anything, I would think that the data corruption
> would happen if the conversion happened _after_ the connection was
> closed.
>
After running into this same memory corruption again, I did a bit more
debugging. Through trial and error, I've determined that it only happens
when I declare a row object and then initialize it later:
mysqlpp::Row row;
while (row = res.fetch_row()) {
...
}
The memory corruption does not appear if I declare the row object inside
the loop condition:
while (mysqlpp::Row row = res.fetch_row()) {
...
}
The tutorial examples clearly imply that the first form is legitimate.
What am I missing here?
Drew Vogel
