SQlite query - How do I retrieve multiple column data? - c++

Question

I'm having great difficulty to find a working example on the net regarding getting multiple values from a SQlite DB using xcode and cocos2dx. Here is the sql query I have:
char sql_query[100];
sprintf(sql_query, "SELECT * FROM SQList WHERE ColumnD BETWEEN %d AND %d ORDER BY RANDOM() LIMIT 1", MinColumnD, MaxColumnD);
The query it self seems to work, the main problem is how do I get the values that I collect from 'select *' into another int or char parameter so that I can use it?
Some example I found referred to using a callback to a struct or mentioned about using sqlite3_prepare_v2 and the step method.
I'm unable to find an example for either methods though, please help!

Answer 1

When using sqlite3_exec, you have to convert all values from strings, and you have to use the callback's void * pointer or some global variable to return data:
struct MyData {
string A;
int B, C;
};
int exec_callback(void *ptr, int argc, char *argv[], char *names[])
{
vector<MyData> *list = reinterpret_cast<vector<MyData> *>(ptr);
MyData d;
d.A = argv[0] ? argv[0] : "";
d.B = atoi(argv[1]);
d.C = atoi(argv[2]);
list->push_back(d);
return 0;
}
void query_with_exec()
{
vector<MyData> list;
char *errmsg = NULL;
sqlite3_exec(db, "SELECT a, b, c FROM SQList /* WHERE ... */",
exec_callback, &list, &errmsg);
if (errmsg) {
printf("error: %s!\n", errmsg);
return;
}
// use list ...
}
When using sqlite3_prepare*, you have to call sqlite3_step in a loop until it does not return SQLITE_ROW anymore (when you expect only one record, you can call it only once):
void query_with_step()
{
vector<MyData> list;
sqlite3_stmt *stmt;
int rc = sqlite3_prepare_v2(db, "SELECT a, b, c FROM SQList /* WHERE ... */",
-1, &stmt, NULL);
if (rc != SQLITE_OK) {
printf("error: %s!\n", sqlite3_errmsg(db));
return;
}
for (;;) {
rc = sqlite3_step(stmt);
if (rc == SQLITE_DONE)
break;
if (rc != SQLITE_ROW) {
printf("error: %s!\n", sqlite3_errmsg(db));
break;
}
MyData d;
const char *text = (const char *)sqlite3_column_text(stmt, 0);
d.A = text ? text : "";
d.B = sqlite3_column_int(stmt, 1);
d.C = sqlite3_column_int(stmt, 2);
list.push_back(d);
}
sqlite3_finalize(stmt);
// use list ...
}

Answer 2

Get the values using "SELECT" query and store your char and int values in an array.Create a NSMUtableArray and store the values which you will get from SELECT query .The following code will help you
-(int)find_putts_count:(int)holeno{
sqlite3 *database;
NSString *databasePath;
NSMUtableArray *arr_tracking_details = [[NSMUtableArray alloc] init];
int putts = -1;
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDir = [documentPaths objectAtIndex:0];
databasePath = [documentsDir stringByAppendingPathComponent:#"GolfElite.sqlite"];
if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK)
{
// Setup the SQL Statement and compile it for faster access
NSString *sqlStatement = nil;
sqlStatement = [NSString stringWithFormat:#"select Putts from Holes WHERE HoleNo == %d and ShotNo == %d and PlayerId == '%#'",holeno,1,[arr_players_id objectAtIndex:scorecard_player_no]];
sqlite3_stmt *compiledStatement;
if(sqlite3_prepare_v2(database, [sqlStatement UTF8String], -1, &compiledStatement, NULL) == SQLITE_OK)
{
if(sqlite3_step(compiledStatement) == SQLITE_ROW)
{
[arr_tracking_details addObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 3)]];
[arr_tracking_details addObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement,6)]];
[arr_tracking_details addObject:[NSString stringWithFormat:#"%d",(int)sqlite3_column_int(compiledStatement, 4)]];
putts = (int)sqlite3_column_int(compiledStatement, 0);
}
}
sqlite3_finalize(compiledStatement);
}
sqlite3_close(database);
return putts;
}