"NSString stringWithFormat:" - Access same parameter multiple times?

Question

When I'm using string formatting, can I access one parameter multiple times without passing it again?

Example:

NSString *parameter1 = @"1";
NSString *parameter2 = @"2";

NSString *myString;
myString = [NSString stringWithFormat:@"I want to print parameter1 here: %@, parameter2 here: %@ and now access parameter1 again: %@ _without_ passing it again.",parameter1, parameter2, parameter1];

Is there a way to access the first parameter again without writing ", parameter1" again?

hamstergene · Accepted Answer · 2012-07-12 14:39:32Z

63

Yes, using positional arguments:

// prints: foo bar foo bar
NSLog(@"%@", [NSString stringWithFormat:@"%2$@ %1$@ %2$@ %1$@", @"bar", @"foo"]);

// NSLog supports it too
NSLog(@"%2$@ %1$@ %2$@ %1$@", @"bar", @"foo");

answered Jul 12, 2012 at 14:39

hamstergene

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3 Comments

mrb Over a year ago

Note that in the format string, you need to refer to all the arguments supplied in the argument list. eg. The following code will cause a bug at runtime, because the first positional argument is unused in the format string: [NSString stringWithFormat:@"%2$@", @"bar", @"foo"] — see stackoverflow.com/questions/2946649/…

hamstergene Over a year ago

@mrb Right. It's side effect of variable arguments (...) implementation in C (not a bug). If you don't tell formatting function what type an argument has (by refering to it at least once), there is no way to correctly locate ones after it.

Add080bbA Over a year ago

i try it with predicateWithFormat but not working. how can use argument position for predicate ?

Max O · Accepted Answer · 2012-07-12 14:41:38Z

4

NSString *parameter1 = @"1";
NSString *parameter2 = @"2";

NSString *myString;
myString = [NSString stringWithFormat:@"I want to print parameter1 here: %1$@, parameter2 here: %2$@ and now access parameter1 again: %1$@ _without_ passing it again.",parameter1, parameter2];

String Format Specifiers

answered Jul 12, 2012 at 14:41

Max O

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