使用sqlite3_column_double检索浮点值 [英] retrieving float values using sqlite3_column_double

问题描述

我对iPhone编程比较陌生，因此如果这看起来很简单，我深表歉意.我试图从SQLite数据库中检索表中的纬度/位置列(FLOAT类型).

I'm relatively new to iPhone programming so I apologize if this seems a simple question. I have latitude/location columns in my table (FLOAT type) that I am trying to retrieve from my SQLite database.

我可以检索基于字符/文本的数据库列，但不知道如何检索浮点值.我应该使用NSString或其他方式格式化属性吗?我希望在CLLocationDistance的更下游使用浮点值.

I can retrieve my character/text based db columns, but don't know how to retrieve my float values. Should I be formatting the attributes using NSString or something else? I wish to use the float values further downstream with CLLocationDistance.

// 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);

推荐答案

经度和纬度是否存储为表中的度数?您的Location对象是否具有CLLocationCoordinate2D属性(例如，将坐标放入其中的坐标)?

Are the latitude and longitude stored as degrees in the table? Does your Location object have a CLLocationCoordinate2D property called, say, coordinates to put the coordinates in?

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

If yes, just set the values directly because CLLocationDegrees is actually just a double. For example:

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

location.coordinates = coords;

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