I have a log file that I'm trying to append data to the end of. I have an NSMutableString
textToWrite
variable, and I am doing the following:
[textToWrite writeToFile:filepath atomically:YES
encoding: NSUnicodeStringEncoding error:&err];
However, when I do this all the text inside the file is replaced with the text in textToWrite. How can I instead append to the end of the file? (Or even better, how can I append to the end of the file on a new line?)
I guess you could do a couple of things:
NSFileHandle *fileHandle = [NSFileHandle fileHandleForWritingAtPath:aPath];
[fileHandle seekToEndOfFile];
[fileHandle writeData:[textToWrite dataUsingEncoding:NSUTF8StringEncoding]];
[fileHandle closeFile];
Note that this will append NSData to your file -- NOT an NSString. Note that if you use NSFileHandle, you must make sure that the file exists before hand. fileHandleForWritingAtPath
will return nil if no file exists at the path. See the NSFileHandle class reference.
Or you could do:
NSString *contents = [NSString stringWithContentsOfFile:filepath];
contents = [contents stringByAppendingString:textToWrite];
[contents writeToFile:filepath atomically:YES encoding: NSUnicodeStringEncoding error:&err];
I believe the first approach would be the most efficient, since the second approach involves reading the contents of the file into an NSString before writing the new contents to the file. But, if you do not want your file to contain NSData and prefer to keep it text, the second option will be more suitable for you.
[Update] Since stringWithContentsOfFile is deprecated you can modify second approach:
NSError* error = nil;
NSString* contents = [NSString stringWithContentsOfFile:filepath
encoding:NSUTF8StringEncoding
error:&error];
if(error) { // If error object was instantiated, handle it.
NSLog(@"ERROR while loading from file: %@", error);
// …
}
[contents writeToFile:filepath atomically:YES
encoding:NSUnicodeStringEncoding
error:&err];