使用sqlite3_column_double检索浮点值

Question

我对iPhone编程比较陌生，所以我很抱歉如果这看起来是一个简单的问题。我在我的表（FLOAT类型），我想从我的SQLite数据库中检索纬度/位置列。

我可以检索我的基于字符/文本的数据库列，但不知道如何检索我的浮点值。我应该使用NSString或其他格式来设置属性的格式吗？我希望使用CLLocationDistance进一步下游的浮点值。

// the array of locations that we will create 
NSMutableArray *locations = [[[NSMutableArray alloc] init] autorelease]; 

const char *sql = "SELECT locations.name, \ 
locations.address, \ 
locations.city, \ 
locations.state, \ 
locations.phone, \ 
locations.zip, \ 
locations.latitude, \ 
locations.longitude \ 
FROM locations \ 
WHERE category = ?1"; 

// the sqlite statement object that will hold our result set 
sqlite3_stmt *statement; 

// prepare the statement to compile the SQL query into byte-code 
int sqlResult = sqlite3_prepare_v2(database, sql, -1, &statement, NULL); 

// reset query before execution 
sqlite3_reset(statement); 

// set bind variable 
sqlite3_bind_text(statement, 1, [categoryParameter UTF8String], -1, SQLITE_TRANSIENT); 

if (sqlResult== SQLITE_OK) { 
    // step through the results - once for each row 
    while (sqlite3_step(statement) == SQLITE_ROW) { 

     // allocate a location object to add to the pharmacies array 
     Location *location = [[Location alloc] init]; 

     // the second parameter is the column index (0 based) in 
     // the result set 
     char *name = (char *)sqlite3_column_text(statement, 0); 
     char *address = (char *)sqlite3_column_text(statement, 1); 
     char *city = (char *)sqlite3_column_text(statement, 2); 
     char *state = (char *)sqlite3_column_text(statement, 3); 
     char *phone = (char *)sqlite3_column_text(statement, 4); 
     char *zipcode = (char *)sqlite3_column_text(statement, 5); 
     float latitude = (float) sqlite3_column_double(statement, 6); 
     float longitude = (float) sqlite3_column_double(statement, 7); 

     // set all attributes of the location 
     location.name = (name) ? [NSString stringWithUTF8String:name] : @""; 
     location.address = (address) ? [NSString stringWithUTF8String:address] : @""; 
     location.city = (city) ? [NSString stringWithUTF8String:city] : @""; 
     location.state = (state) ? [NSString stringWithUTF8String:state] : @""; 
     location.phone = (phone) ? [NSString stringWithUTF8String:phone] : @""; 
     location.zipcode = (zipcode) ? [NSString stringWithUTF8String:zipcode] : @""; 

     [locations addObject:location]; 
     [location release]; 
    } 

    // finalize the statement to release its resources 
    sqlite3_finalize(statement); 

Answer 1

纬度和经度是以度表的形式存储的吗？你的Location对象是否有一个名为CLLocationCoordinate2D的属性，比如坐标来放置坐标？

如果是，直接设置值，因为CLLocationDegrees实际上只是一个双精度值。例如：

CLLocationCoordinate2D coords; 
coords.latitude = sqlite3_column_double(statement, 6); 
coords.longitude = sqlite3_column_double(statement, 7); 

location.coordinates = coords;