QSqlQuery doesn't answer correctly - c++

Question

I tried to create a SQLite database with Qt and and I did!! I called my db "prova_db" and it contains the following table:
marker_db
id site (columns)
0 www.google.it
1 www.youtube.it
2 www.facebook.it
Then, I tried to query my prova_db. Here is code:
int main () {
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("prova_db");
if (!db.open()) { printf("DB doesn't exist\n");}
else {
QSqlQuery query1;
query1.exec( "SELECT site FROM marker_db WHERE id = 1");
int i = query1.numRowsAffected();
printf("result row: %d\n", i);
while(query1.next()){
QString str = query1.value(0).toString();
printf("result: %s\n", str);
}
}
db.close();
return 0;
}
The result is:
result row : 0
result : (strange char)
instead the result should be:
result row: 1
result : www.youtube.it
where am I doing wrong??
Thank you!

Answer 1

I think you have the wrong expectation: the result of numRowsAffected() tells you how many rows have been altered by the query. Your query does not alter anything, so the result should be either 0 or undefined. Thus, you shouldn't expect the first output to be risultato riga: 1. Use the size() method instead to find out how many rows have matched your SELECT query.
The second problem is that you are passing a QString object to printf(), which expects a pointer to a null-terminated array of char values instead (when you use the %s format specifier). You need to convert the QString object into a pointer to a C array of characters.