Logging to a file on the iPhone

Question

What would be the best way to write log statements to a file or database in an iPhone application?

Ideally, NSLog() output could be redirected to a file using freopen(), but I've seen several reports that it doesn't work. Does anyone have this going already or have any ideas how this might best be done?

Thanks!

Answer 1

I've successfully used freopen(...) on the phone to re-direct output to my own file.

Answer 2

This code works for me:

- (void)applicationDidFinishLaunching:(UIApplication *)application {
#if TARGET_IPHONE_SIMULATOR == 0
    freopen([@"/tmp/my_logs.txt" fileSystemRepresentation], "w", stderr);
#endif
}

Answer 3

If you want to use Cocoa, NSString and NSData have methods for reading/writing to file and NSFileManager gives you file operations. Here's an example (should work on iPhone):

NSData *dataToWrite = [[NSString stringWithString:@"String to write"] dataUsingEncoding:NSUTF8StringEncoding];

NSString *docsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *path = [docsDirectory stringByAppendingPathComponent:@"fileName.txt"];

// Write the file
[dataToWrite writeToFile:path atomically:YES];

// Read the file
NSString *stringFromFile = [[NSString alloc] initWithContentsOfFile:path];  

// Check if file exists
NSFileManager *fileManager = [NSFileManager defaultManager];
[fileManager fileExistsAtPath:path]; // Returns a BOOL    

// Remove the file
[fileManager removeItemAtPath:path error:NULL];

// Cleanup
[stringFromFile release];
[fileManager release];

Answer 4

This code works great for me..

#if TARGET_IPHONE_SIMULATOR == 0
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *logPath = [documentsDirectory stringByAppendingPathComponent:@"console.log"];
    freopen([logPath cStringUsingEncoding:NSASCIIStringEncoding],"a+",stderr);
#endif

You can then get the log file off the iphone using the method outlined here http://blog.coriolis.ch/2009/01/09/redirect-nslog-to-a-file-on-the-iphone/#more-85

Note that using freopen will STOP THE CONSOLE IN XCODE working.. however, for some reason the console you can view in xcode's organiser still works great.

Answer 5

Consider using Cocoa Lumberjack. It's a light but flexible utility to replace NSLog functionality. In my opinion it's in the same class as Log4J, allowing for custom appenders and the like. It has an SQLite logger, for example.