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trying to figure out how to add zeroes in front of a random generated number with dynamic length of the number. For example if the number is 10 characters long, I can print the number as stringWithFormat:@"%.10d",i

Since the numer can somtimes be shorter than maximum length, it needs zeroes to fill the maximum length of the number to fit the string.

- (void)method:(int)length{
int i = rand() % length;
NSLog (@"%@",[NSString stringWithFormat:@"%.'length'd",i]);
}
linge
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1 Answers1

15
NSLog (@"%@",[NSString stringWithFormat:@"%010d",i]);

The meaning of format string components:

  • 1st 0 - means that the number must be padded to specific width with zeros
  • 10 - required minimum width of output

For more information about format specifiers you can check this printf specification. I sometimes also use this shorter one - you can find your example there.

You can create your format string dynamically as well - you'll need to calculate maximum number length in advance (maxLength in example): 

NSString* format = [NSString stringWithFormat:@"%%0%dd", maxLength];
NSString *s = [NSString stringWithFormat:format, 10];
NSLog(@"%@", s);
Vladimir
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  • Thanks for the format specifier info. But the dynamic length still remains a question. Is it possible to get the required minimum width of the output to be dynamic depending on the maximum length of the number that should be padded? Example result max_length 1000 (4 digits) - result 0042 max_length 100000 (6 digits) - result 003491 – linge Aug 22 '10 at 13:36
  • +1 for the links to compact + detailed printf specifications. I struggled to find them via google, but found them easily with your answer - thanks! – Adam Aug 20 '13 at 14:37