Log to a custom file, can be used to get logs from users with a debug build.

FileLogging.h

#ifndef FILELOGGING
#define FILELOGGING

#ifndef DEBUG
#define FLOG(args...)
#else
#define kLOGFILEPATH @"/path/to/log/file.log"

void _FLog(const char *functionName, int lineNumber, NSString *msgFormat, ...) {
	va_list ap;
	va_start(ap, msgFormat);
	NSString *logFormattedMessage = [[NSString alloc] initWithFormat:msgFormat arguments:ap];
	va_end(ap);
	NSString *logMessage = [NSString stringWithFormat:@"%s[%d] %@\n", functionName, lineNumber, logFormattedMessage];
#if !__has_feature(objc_arc)
	[logFormattedMessage release];
#endif
	if (![[NSFileManager defaultManager] fileExistsAtPath:kLOGFILEPATH])
		[[NSData data] writeToFile:kLOGFILEPATH atomically:YES];
	NSFileHandle *handle = [NSFileHandle fileHandleForWritingAtPath:kLOGFILEPATH];
	[handle truncateFileAtOffset:[handle seekToEndOfFile]];
	[handle writeData:[logMessage dataUsingEncoding:NSUTF8StringEncoding]];
	[handle closeFile];
}

#define FLOG(args...) _FLog(__func__, __LINE__, args);
#endif // DEBUG

#endif // FILELOGGING