Hi everyone,

I hope this has not been asked before, I searched the online archives of
the list and could not find any references to my problem.

I'm trying to run a simple test program based on the simple1 example. I
can get connected to the DB, I create a query and execute it. q.size()
return 4 wich is the number of row I expected so the query is fine. Then
I try to enumerate the result of the query like this :

<code>
mysqlpp::Row row;
mysqlpp::Row::size_type i;
for (i = 0; row = res.at(i); ++i)
cout <<row.at(0) <<endl;
</code>

however I get an length_error exception on "row = res.at(i)".

Since I'm new to MySQL++, maybe i'm doing something stupid and someone
can point me to it.

Thanks in advance.

Mathieu Pagé








Complete code :
#include <mysql++.h>

#include <iostream>
#include <exception>

using namespace std;

int main(int argc, char* argv[])
{
try
{
// On se connecte à la DB
mysqlpp::Connection con(true);
con.connect("chess", "localhost", "root", "SomePassword");

if (!con)
{
cout <<"erreur" <<endl
<<con.error() <<endl;

return 1;
}

// On créer une requête
mysqlpp::Query q = con.query();
q <<"SELECT NomJoueur FROM tblJoueurs";

// On exécute la requête
mysqlpp::Result res = q.store();

cout <<"Il y as : " <<res.size() <<" lignes." <<endl;

// On affiche la liste des joueurs
if (res && res.size() > 0)
{
mysqlpp::Row row;
mysqlpp::Row::size_type i;
for (i = 0; row = res.at(i); ++i)
{
cout <<row.at(0) <<endl;
}
}
else
{
cout <<"Erreur dans la requête : " <<q.error() <<endl;
return 1;
}


}
catch (mysqlpp::ConnectionFailed e)
{
cout <<e.what() <<endl;
}

return 0;
}

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Mathieu Pagé wrote:
I think you're expecting Row::at() to return false (or, rather, an
object that can be converted to false) when you walk off the end of the
result set. MySQL++ doesn't do that sort of thing, by design. It
signals errors with exceptions, just as you saw.

That is the fall-back behavior when you turn off exceptions, however.
Read the user manual for details.

You might also look at examples/simple3.cpp. It operates in a way very
similar to what you're doing, without needing special treatment. It
does that by using a different type of query than you are using.

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Warren Young a écrit :

Thanks you for your answer.

I looked at simple.cpp and tried to do the same thing in my code (using
"res.fetch_row()") and I got the same error. Actually I just realised,
looking at the stack trace when the error occurs, that the exception is
trown during the execution of the operator= function that copy the row.

I also tried to execute example/resetdb tonight and it raise an
exception too. Maybe there is a problem with my compiled version of MySQL++.

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Warren Young a écrit :

Thanks anyway for trying to help. It was appreciated.

It turns out I was not using the right mysql++.lib files. I was using a
release one to link into a debug executable. That's what caused the
exception, probably because the object structures were differents
between a realease and debug build.

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Mathieu Pagé wrote:
Yep. That'll cause all kinds of havoc.

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