Re: Can you have more than one active mysqlpp::Connection object?

[Byrial Jensen]

Chris Frey wrote:
> On Wed, May 25, 2005 at 11:37:07AM -0700, Earl Miles wrote:
> 
>>From looking this over, I think your problem might be string manipulation.
>>
>>const char *text = row[1];
>>
>>I'm not sure row[] is guaranteed to return a null terminated string. 

Now I have studied the mysql++ source code. row[] returns a temporary 
ColData object and that object have a function to do conversion to 
"const char *" which indeed gives a pointer to a NUL-terminated string.

However - as Chris points out - the ColData object is destructed 
immidiately after the conversion, leaving the string pointer pointing to 
freed memory, which caused all the trouble.

> Yep, Earl is on the right track.  See the declaration of operator[] in
> row.h:
> 
> const ColData   operator [] (size_type i) const;
> 
> This returns a temporary, which disappears after that line of code.
> You need to make a copy for yourself.

I replaced the line

   const char *text = row[1];

with

    const ColData text_col = row[1];
    const char *text = text_col;

and that fixed all observed problems in my programs. Thank you very much 
for the suggestion.

I don't know if it is considered a bug that you cannot write

    const char *text = row[1];

but even if it isn't, it might be an idea to warn about the construction 
in the manual.

Thanks to all helpful people in this thread.

Best regards
Byrial