NSLog

void NSLog(NSString *format, ...);

NSLog works basically like:

fprintf(stderr, format_string, args ...);

But its format string is a NSString object rather than simple char *. You can use it in the predictable ways:

NSLog(@"ALL YOUR BASE ARE BELONG TO US");
NSLog(@"x = %d, y = %d", x, y);
NSLog(@"%s\t%s\t0x%08x", "hex", "value", 0x1243);

NSLog will also display meaningful values for well known objects as well:

NSLog(@"my ns string = %@", myNSString);
NSLog(@"my dictionary = %@", myDict);
NSLog(@"my image = %@", myNSImage);

NSLog works in this case by asking each object for a string that describes itself, sending the -description method to the objects. (Note: if an object doesn't implement the description method, you tend to get are result like this <classname : address>. See UsingTheDescriptionMethod

NSLog is very nice, but be careful which specifier you use. Consider the following:

int i = 12345;
NSLog( @"%@", i );   //  Signal 10 SIGBUS error

NSLog( @"%d", i );

i (an int) is not an object! So you can't send description to it (see above)

True, but you could make it one with NSNumber, if you wanted to, like so.

NSLog(@"%@", [NSNumber numberWithInt:i]);

--CharlieMiller

NSLog format specifiers:

%@     Object
%d, %i signed int
%u     unsigned int
%f     float/double

%x, %X hexadecimal int
%o     octal int
%zu    size_t
%p     pointer
%e     float/double (in scientific notation)
%g     float/double (as %f or %e, depending on value)
%s     C string (bytes)
%S     C string (unichar)
%.*s   Pascal string (requires two arguments, pass pstr[0] as the first, pstr+1 as the second)
%c     character
%C     unichar

%lld   long long
%llu   unsigned long long
%Lf    long double

"Object" refers to a Cocoa object (responding to -description) or a Core Foundation object. For more, see man 3 printf. NSLog understands all printf format specifiers as well as %@ and %C.

Alternatives to NSLog:

XLog is an alternative if you think the header is to wide or you would like to log the elapsed time from the previous log.

ZNLog? http://codebeach.org/code/show/44

LibComponentLogging is a small library for Objective-C applications on Mac OS X and the iPhone OS which provides log levels, log components for identifying different parts of an application, and an active log level for each log component in order to enable/disable logging for certain parts of an application. Additionally, different logging backends are available, e.g. one which writes to a rotating log file, and one which sends log messages to the Apple System Log facility (ASL). See http://0xc0.de/LibComponentLogging for details.

BTTimeLog? is a simple Objective-C class I put together that logs the time used by an application. The output includes a logging level, accumulated and differential times, the class and method that made the call, and a user string with arguments. More at http://steveweller.com/articles/speedup/

See NSLogToFile for redirecting NSLog output.