Question

When I’m saving a simple text file from my iPhone app as NSUTF16StringEncoding, it seems to like adding an extra ‘space’ at the start of each new line that I add. This is some rough code detailing what I’m doing (not exact, and not necessarily executable as is).

NSArray *paths          = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES);
NSString *tempPath      = [paths objectAtIndex:0];
NSString *tempFilename  = [NSString stringWithFormat:@"%ld", (long)[[NSDate date] timeIntervalSince1970]];
NSString *tempFilePath  = [tempPath stringByAppendingPathComponent:tempFilename];
NSError *error;

freopen([tempFilePath cStringUsingEncoding:NSASCIIStringEncoding],"a+",stderr);
NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:tempFilePath];

NSString *testLine1 = @"test row 1";
[fileHandle seekToEndOfFile];
[fileHandle writeData:[testLine1 dataUsingEncoding:NSUTF16StringEncoding]]; // NSUTF8StringEncoding

NSString *testLine2 = @"test row 2";
[fileHandle seekToEndOfFile];
[fileHandle writeData:[testLine2 dataUsingEncoding:NSUTF16StringEncoding]]; // NSUTF8StringEncoding

NSString *testLine3 = @"test row 3";
[fileHandle seekToEndOfFile];
[fileHandle writeData:[testLine3 dataUsingEncoding:NSUTF16StringEncoding]]; // NSUTF8StringEncoding

[fileHandle closeFile];  

// convert csv text to data
NSData *dataCsvOutput = [NSData dataWithContentsOfFile:tempFilePath];

NSArray *objects  = [NSArray arrayWithObjects:dataCsvOutput, exportFilename, deviceType, nil];        
NSArray *keys     = [NSArray arrayWithObjects:@"data", @"filename", @"devicetype", nil];
NSDictionary *dictionary = [NSDictionary dictionaryWithObjects:objects 
                                                   forKeys:keys];            

NSString  *exportFilename = [withDictionary objectForKey:@"filename"];
NSData    *dataCsvOutput  = [withDictionary objectForKey:@"data"];
NSString  *deviceType     = [withDictionary objectForKey:@"devicetype"];

MFMailComposeViewController *mfViewController = [[MFMailComposeViewController alloc] init];
mfViewController.mailComposeDelegate          = self;
[mfViewController setSubject:@"Test"];
[mfViewController setMessageBody:[NSString stringWithFormat:@"Please find data attached."] isHTML:NO];
[mfViewController addAttachmentData:dataCsvOutput mimeType:@"text/plain;charset=utf-16" fileName:exportFilename];
[self presentModalViewController:mfViewController animated:YES];
[mfViewController release];  

The resulting text file ends up being something like:

test row 1
 test row 2
 test row 3

Can anyone suggest why that is ? It works fine when exported as UTF-8.

Thanks.

Answer 1

NSUTF16StringEncoding (which is an alias to NSUnicodeStringEncoding) prepends the output with a so-called “byte-order marker”, which consists of the bytes “FE FF” or “FF FE” and indicates whether the following data is big-endian or little-endian UTF-16.

To avoid the byte-order marker, use either NSUTF16BigEndianStringEncoding or NSUTF16LittleEndianStringEncoding.

Remark: A better alternative for

[tempFilePath cStringUsingEncoding:NSASCIIStringEncoding]

is

[tempFilePath fileSystemRepresentation];