About the formation in NSLog in Objective-C

Question

const char *string ="Hi there,this is a C string";
NSData *data=[NSData dataWithBytes:string 
                            length:strlen(string)+1];
NSLog(@"data is %@",data);
NSLog(@"%lu byte string is '%s'",[data length],[data bytes]);

This can be implied successfully. If the last sentence is:

NSLog(@"%d byte string is '%s'",[data length],[data bytes]);

it will warn that conversion specifies type 'int' but argument has typed 'NSUInteger' (aka'usigned long')

Why %d can't?

Take a look at http://stackoverflow.com/a/6727693/944634 – Parag Bafna Jul 15 '12 at 05:27 — Parag Bafna, Jul 15 '12 at 05:27

score 2 · Accepted Answer · answered Jul 15 '12 at 03:10

2

NSUInteger is basically an unsigned long, so use %lu instead.

answered Jul 15 '12 at 03:10

TheAmateurProgrammer

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but the question is y the '%d' can't .The textbook wrote it. – Lucas Huang Jul 15 '12 at 03:15
1

I don't know what textbook you're reading, but in ObjC you need to pass the correct "long/short" and "signed/unsigned" in the format specifier. %lu is correct (long unsigned). %d (short, signed) is not. – Rob Napier Jul 15 '12 at 03:43
thank you for you answer. Perhaps the textbook has to be improved or the translators.Thank you! – Lucas Huang Jul 15 '12 at 11:18

score 0 · Answer 2 · answered Jul 15 '12 at 03:56

0

%d means 'int'. NSUInteger is not an 'int', so %d won't work. You have to match format specifiers with the type. If you specify the wrong type, your program can crash or more likely, it'll print garbage.

answered Jul 15 '12 at 03:56

Graham Perks

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%d is for ints. %f for doubles. All the specifiers are documented here: https://developer.apple.com/library/mac/ipad/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html – Graham Perks Jul 15 '12 at 14:03

About the formation in NSLog in Objective-C

2 Answers2