NSString转换到NSDate时日期不对

代码：

NSString * dateStr = @"7/25/2013 12:00:00 AM";    
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"MM/dd/yyyy hh:mm:ss a"];
NSDate *date = [dateFormat dateFromString:dateStr];  
NSLog(@"dateStr : %@ , date : %@",dateStr,date);

但是转换的日期会比实际日期差一天：

dateStr : 7/25/2013 12:00:00 AM , date : 2013-07-24 18:30:00 +0000

NSString * dateStr = @"7/25/2013 12:00:00 AM";

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"MM/dd/yyyy hh:mm:ss a"];
 [dateFormat setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
NSDate *date = [dateFormat dateFromString:dateStr];

NSLog(@"dateStr : %@ , date : %@",dateStr,date);

试试看

 NSString * dateStr = @"7/25/2013 12:00:00 AM";

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
 [dateFormat setTimeZone:[NSTimeZone timeZoneWithName:@"UTC"]];
    [dateFormat setDateFormat:@"MM/dd/yyyy hh:mm:ss a"];
    NSDate *date = [dateFormat dateFromString:dateStr];