How to dynamically build up the arguments for NSLog?

Question

Example: I have a complex method that does a lot of stuff, and at the end I want to print a report with NSLog. NSLog wants a string, and then an arbitrary number of arguments. So lets say there are these possible values which can be logged:

A

B

C

D

E

F

It can happen that -for example- C and D are not logged, but the whole rest. How would I build up a dynamic thing which represent the value arguments for NSLog?

I choose NSLog for this question because it may be simpler aus NSPredicate and SUBQUERY. It seems impossible to build an NSPredicate format string dynamically while using an NSMutableString and appendFormat:... it results always in compile errors for the predicate. I guess that NSPredicate does something different with it's provided format values than NSMutableString -appendFormat does.

So if there was a way to feed NSPredicate with: 1) a huge, dynamically created format string 2) an huge, dynamically created "list" of arguments"

that would be cool.

Answer 1

Something like this should do it, conditionally append parts to the string:

NSMutableString* logMsg = [NSMutableString stringWithFormat:@"%@ %@ %@", A, B, C];

if (C) [logMsg appendFormat:@" %@", C];
if (D) [logMsg appendFormat:@" %@", D];

[logMsg appendFormat:@" %@ %@", E, F];

NSLog(@"%@", logMsg);

Answer 2

Your underlying problem shouldn't be a problem. Just use +predicateWithFormat:argumentArray:. What issue are you having building this up?

Answer 3

If you're collecting a variable list of strings to be output at one time, simply use a NSMutableArray adding a line of log output as needed. Then at the end of the process, joing the components with a string:

NSMutableArray *logLines = [[NSMutable alloc] initWithCapacity:10];
...
NSLog(@"Multiple-line output:\n%@",[logLines componentsJoinedByString:@"\n"]);
[logLines release];