How to check if mysql query was successful using C++ - c++

Question

I'm using a C++ interpreter (ROOT, the CERN framework) to access several mySQL tables in a loop. Every time I query a table that doesn't exist, the program quits on me:
for (int run = 19000; run < 22000; run ++) {
s << run;
num = s.str();
schema = "run_0"+num+"_R007";
s.str("");
//creating our query
query = "select distinct *whatever* from "+schema+".kTrack;";
res = conPtr->Query(query);
conPtr->Close();
//Here is where I don't know what to do:
if (*success*) {
do stuff
}
else {
do stuff
}
}
I don't have a problem if the table returns 0 rows, I have a problem if the table doesn't exist.
What is wrong with my code?

Answer 1

Assuming conPtr is a pointer to a TMySQLServer object, ROOT's documentation for TMySQLServer::Query() says:
Returns a pointer to a TSQLResult object if successful, 0 otherwise. The result object must be deleted by the user.
So Query() returns a NULL pointer on failure.
Also, since your loop is not re-opening a new DB connection on each iteration, you should not be calling conPtr->Close() until after you are done performing queries with it.
Try something more like this:
for (int run = 19000; run < 22000; run ++) {
s << run;
num = s.str();
schema = "run_0"+num+"_R007";
s.str("");
//creating our query
query = "select distinct *whatever* from "+schema+".kTrack;";
res = conPtr->Query(query);
if (res) {
// use res as needed...
delete res;
}
else {
// ...
}
}
conPtr->Close();