我正在尝试阅读 float value ，我将其值更新为 SQLite数据库。我用 REAL作为一种浮点值。以下是我用来更新SQLite的代码:

//update download percent
sqlite3_stmt    *statement;
const char *dbpath = [databasePath UTF8String];

if (sqlite3_open(dbpath, &myDB) == SQLITE_OK)
{
    const char *update_stmt = [[NSString stringWithFormat:@"UPDATE myTable SET floatValueColumn=%f WHERE id=%i", myProgress, myTargetId] UTF8String];

    if( sqlite3_prepare_v2(myDB, update_stmt, -1, &statement, NULL) == SQLITE_OK )
    {
        if(SQLITE_DONE != sqlite3_step(statement)){ //sql fail

            NSLog(@"error: %s", sqlite3_errmsg(myDB));
        }
        sqlite3_reset(statement);
        // Finalize and close database.
        sqlite3_finalize(statement);
    }
    // close database
    sqlite3_close(myDB);
}

NSString *docsDir;
NSArray *dirPaths;

// Get the documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

docsDir = [dirPaths objectAtIndex:0];

// Build the path to the database file
databasePath = [[NSString alloc]
                initWithString: [docsDir stringByAppendingPathComponent:
                                 @"mydbs.db"]];

NSFileManager *filemgr = [NSFileManager defaultManager];

if ([filemgr fileExistsAtPath: databasePath ] == NO)
{
    const char *dbpath = [databasePath UTF8String];

    if (sqlite3_open(dbpath, &myDB) == SQLITE_OK)
    {
        char *errMsg;
        const char *sql_stmt =
        "CREATE TABLE IF NOT EXISTS MYTABLE (MYFLOATVALUECOLUMN REAL)";

        if (sqlite3_exec(myDB, sql_stmt, NULL, NULL, &errMsg) != SQLITE_OK)
        {
            //alert
        }
        sqlite3_close(myDB);
    } else {
        //alert
    }
}

最佳答案

几件事:

//  ViewController.m
//  sqlite demo

#import "ViewController.h"
#import <sqlite3.h>

@interface ViewController ()
{
    sqlite3 *database;
}

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self testSqlite];
}

#pragma mark - SQLite methods

// test my database interaction

- (void)testSqlite
{
    if (![self openDb])
        return;

    if (![self dropTable])
    {
        [self closeDb];
        return;
    }

    if (![self createTable])
    {
        [self closeDb];
        return;
    }

    double initialStoredValue = 0.1;
    sqlite3_int64 rowId = [self insertRowWithDouble:initialStoredValue];
    if (rowId < 0)
    {
        [self closeDb];
        return;
    }

    double retrievedValue = [self selectDoubleForRow:rowId];
    NSLog(@"%s inserted row with value of %f, retrieved value of %f", __FUNCTION__, initialStoredValue, retrievedValue);

    double newValue = 0.2;
    if (![self updateRow:rowId withDouble:newValue])
    {
        [self closeDb];
        return;
    }

    retrievedValue = [self selectDoubleForRow:rowId];
    NSLog(@"%s updated row with value of %f, retrieved value of %f", __FUNCTION__, newValue, retrievedValue);

    if (![self closeDb])
        return;
}

// return TRUE if successful, FALSE if not

- (BOOL)openDb
{
    NSString *documentsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
    NSString *databasePath = [documentsPath stringByAppendingPathComponent:@"vdos.db"];

    if (sqlite3_open([databasePath UTF8String], &database) != SQLITE_OK)
    {
        NSLog(@"%s database open failed", __FUNCTION__);
        return FALSE;
    }

    return TRUE;
}

// return TRUE if successful, FALSE if not

- (BOOL)dropTable
{
    const char *sql = "DROP TABLE IF EXISTS mytable";
    char *errmsg;

    if (sqlite3_exec(database, sql, NULL, NULL, &errmsg) != SQLITE_OK)
    {
        NSLog(@"%s table drop failed: \"%s\"", __FUNCTION__, errmsg);
        return FALSE;
    }

    return TRUE;
}

// return TRUE if successful, FALSE if not

- (BOOL)createTable
{
    const char *sql = "CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY AUTOINCREMENT, float_column REAL)";
    char *errmsg;

    if (sqlite3_exec(database, sql, NULL, NULL, &errmsg) != SQLITE_OK)
    {
        NSLog(@"%s table create failed: \"%s\"", __FUNCTION__, errmsg);
        return FALSE;
    }

    return TRUE;
}

// return the primary key of the inserted table
//   -1 = failure

- (sqlite3_int64)insertRowWithDouble:(double)value
{
    sqlite3_stmt *statement;
    const char *sql = "INSERT INTO mytable (float_column) VALUES (?)";

    if (sqlite3_prepare(database, sql, -1, &statement, NULL) != SQLITE_OK)
    {
        NSLog(@"%s prepare failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return -1;
    }

    if (sqlite3_bind_double(statement, 1, value) != SQLITE_OK)
    {
        NSLog(@"%s column bind failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return -1;
    }

    if (sqlite3_step(statement) != SQLITE_DONE)
    {
        NSLog(@"%s step failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return -1;
    }

    if (sqlite3_finalize(statement) != SQLITE_OK)
    {
        NSLog(@"%s finalize failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return -1;
    }

    return sqlite3_last_insert_rowid(database);
}

// return float_column value for row with particular rowId

- (double)selectDoubleForRow:(sqlite3_int64)rowId
{
    sqlite3_stmt *statement;
    const char *sql = "SELECT float_column FROM mytable WHERE id = ?";

    if (sqlite3_prepare(database, sql, -1, &statement, NULL) != SQLITE_OK)
    {
        NSLog(@"%s prepare failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return FALSE;
    }

    if (sqlite3_bind_int64(statement, 1, rowId) != SQLITE_OK)
    {
        NSLog(@"%s column bind failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        sqlite3_finalize(statement);
        return FALSE;
    }

    if (sqlite3_step(statement) != SQLITE_ROW)
    {
        NSLog(@"%s step failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        sqlite3_finalize(statement);
        return FALSE;
    }

    double value = sqlite3_column_double(statement, 0);

    if (sqlite3_finalize(statement) != SQLITE_OK)
    {
        NSLog(@"%s finalize failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return FALSE;
    }

    return value;
}

// return the primary key of the inserted table
//   -1 = failure

- (BOOL)updateRow:(sqlite3_int64)rowId withDouble:(double)value
{
    sqlite3_stmt *statement;
    const char *sql = "UPDATE MYTABLE SET float_column = ? WHERE id = ?";

    if (sqlite3_prepare(database, sql, -1, &statement, NULL) != SQLITE_OK)
    {
        NSLog(@"%s prepare failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return FALSE;
    }

    if (sqlite3_bind_double(statement, 1, value) != SQLITE_OK)
    {
        NSLog(@"%s column bind 1 failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        sqlite3_finalize(statement);
        return FALSE;
    }

    if (sqlite3_bind_int64(statement, 2, rowId) != SQLITE_OK)
    {
        NSLog(@"%s column bind 2 failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        sqlite3_finalize(statement);
        return FALSE;
    }

    if (sqlite3_step(statement) != SQLITE_DONE)
    {
        NSLog(@"%s step failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        sqlite3_finalize(statement);
        return FALSE;
    }

    if (sqlite3_finalize(statement) != SQLITE_OK)
    {
        NSLog(@"%s finalize failed: \"%s\"", __FUNCTION__, sqlite3_errmsg(database));
        return FALSE;
    }

    return TRUE;
}

// return TRUE if successful, FALSE if not

- (BOOL)closeDb
{
    if (sqlite3_close(database) != SQLITE_OK)
    {
        NSLog(@"%s database close failed", __FUNCTION__);
        return FALSE;
    }

    database = NULL;

    return TRUE;
}

@end

// return TRUE if successful, FALSE if not

- (BOOL)createTableBad
{
    const char *sql = "CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY AUTOINCREMENT, float_column INTEGER)";
    char *errmsg;

    if (sqlite3_exec(database, sql, NULL, NULL, &errmsg) != SQLITE_OK)
    {
        NSLog(@"%s table create failed: \"%s\"", __FUNCTION__, errmsg);
        return FALSE;
    }

    return TRUE;
}

// return TRUE if successful, FALSE if not

- (BOOL)createTableReallyBad
{
    const char *sql = "CREATE TABLE IF NOT EXISTS mytable (id INTEGER PRIMARY KEY AUTOINCREMENT, float_column HIPPOPOTOMUS)";
    char *errmsg;

    if (sqlite3_exec(database, sql, NULL, NULL, &errmsg) != SQLITE_OK)
    {
        NSLog(@"%s table create failed: \"%s\"", __FUNCTION__, errmsg);
        return FALSE;
    }

    return TRUE;
}

关于iphone - 更新 SQLite 中的浮点值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13737203/