I'm writing a parser for fortune files. Fortune is a small app on *nix platforms that just prints out a random "fortune". The fortune files are straight text, with each fortune being separated by a percent sign on its own line. For example:
A little suffering is good for the soul.
-- Kirk, "The Corbomite Maneuver", stardate 1514.0
A man either lives life as it happens to him, meets it head-on and
licks it, or he turns his back on it and starts to wither away.
-- Dr. Boyce, "The Menagerie" ("The Cage"), star date unknown
@"A little suffering is good for the soul.\n\t\t-- Kirk, \"The Corbomite Maneuver\", stardate 1514.0\n%\nA man either lives life as it happens to him, meets it head-on and\nlicks it, or he turns his back on it and starts to wither away.\n\t\t-- Dr. Boyce, \"The Menagerie\" (\"The Cage\"), stardate unknown\n%"
fileManager = [NSFileManager defaultManager];
// NSString *fileContents = [NSString stringWithContentsOfFile:fileName encoding:NSASCIIStringEncoding error:nil];
NSString *fileContents = [NSString stringWithContentsOfFile:fileName usedEncoding:&stringEncoding error:nil];
NSArray *fileLines = [fileContents componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]];
You are calling
NSLog() but passing the line strings as the format string. Something like:
Therefore, any percent characters in the line strings are interpreted as format specifiers. You should (almost) never pass strings that come from outside sources — i.e. strings which are not hard-coded in your code — as format strings to any function (
+[NSString stringWithFormat:], etc.). It's not safe and you'll sometimes get unexpected results like you've seen.
You should always log a single string like this:
That is, you need to pass a hard-coded format string and use the foreign string as data for that to format.