How to call and convert an int/NSNumber when calling on a sqlite3 database in Objective-C?

Question

Thanks in advance for taking your time out for reading and hoping to assist me. I am relatively new to coding and the current problem I am facing is;

I have built a sqlite3 database, with three columns which are respectively stored as; string, float and an int. When trying to read and represent the columns, I am having trouble in finding a method in order to represent the float and int values.

The three properties which are stores in the database are set as;

@property (nonatomic, strong) NSString *name;
@property (nonaomtic, strong) NSNumber *price;
@property (nonaomtic, strong) NSNumber *quantity;

I'm not sure if maybe changing the latter two properties into float and int would make a difference?

However, the main confusion for me lies in the following code I have made in order to call on the data base;

-(void)readDataFromDatabase{
[self.stock removeAllObjects];

sqlite3 *database;

if (sqlite_open([self.databasePath UTF8String], &database) == SQLITE_OK) {
   char *sqlStatement = "select * from entries";
   sqlite3_stmt *compiledStatement;

if (sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK){
   while(sqlite3_step(compiledStatement) == SQLITE_ROW{
      char *n = sqlite3_column_text(compiledStatement, 1);
      char *p = sqlite3_column_int(compiledStatement, 2);
      chat *q = sqlite3_column_int(compiledStatement, 3);

      NSString *name = [NSString stringWithUTF8String:n];
      NSNumber *price = [NSString stringWithUTF8String:p];
      NSNumber *quantity = [NSString stringWithUTF8String:q];

      Data *data = [[Data alloc] initWithData:name thePrice: price theQuantity:quantity];
      [self.stock addObject:data];
    }
  }
  sqlite3_finalize(compiledStatement);
}
sqlite3_close(database);
}

My common sense tells me the problem lies in this section;

NSString *name = [NSString stringWithUTF8String:n];
NSNumber *price = [NSString stringWithUTF8String:p];
NSNumber *quantity = [NSString stringWithUTF8String:q];

I'm not sure how I should approach the NSNumber? I'm aware the NSString stringWithUTF8String is not correct, but I don't know the equivalent for NSNumber.

I would really appreciate any insight and help on this matter.

Thank you!

Answer 1

You are on the right track with what you've mentioned for float and int. Float does not need to be referenced like NSString because it's size does not vary between 32-bit and 64-bit systems. If your integer is larger then I would recommened using NSInteger for that value:

char *n = sqlite3_column_text(compiledStatement, 1);
float p = sqlite3_column_text(compiledStatement, 2);
int q = sqlite3_column_text(compiledStatement, 3);

NSString *name = [NSString stringWithUTF8String:n];
float price = p;
NSInteger quantity = q;

Note: You don't the * for the float or int values, since they are not pointers.

You might even be able just to do (If you are already declaring the properties in your header):

name = [NSString stringWithUTF8String:sqlite3_column_text(compiledStatement, 1)];
price = sqlite3_column_text(compiledStatement, 2);
quantity = sqlite3_column_text(compiledStatement, 3);

To check the values you can use NSLog:

NSLog(@"%@ %.02f %li", name, price, quantity);

For completeness sake, if you wanted to make the float and int into NSNumber:

NSString *name = [NSString stringWithUTF8String:n];
NSNumber *price = [NSNumber numberWithFloat:p];
NSNumber *quantity = [NSNumber numberWithInt:q];

With the properties in your header declared:

name = [NSString stringWithUTF8String:n];
value = [NSNumber numberWithFloat:p];
quantity = [NSNumber numberWithInt:q];

NSLog(@"%@ %@.02f %@", name, price, quantity);

There are multiple ways to get your result, and that's what makes Objective-C quite flexible.