Padding string to left

Question

How can one pad a string to left in objective c. E.g if I have an integer value of 6 I want it to be displayed as 06.

I use stringByPaddingToLength: but

Answer 1

for completness (using * placeholder):

NSString *paddedNumberString = [NSString stringWithFormat:@"%0*d", amountOfZeros, numberNSInteger]

Answer 2

+ (NSString *)formatValue:(int)value forDigits:(int)zeros {
    NSString *format = [NSString stringWithFormat:@"%%0%dd", zeros]; 
    return [NSString stringWithFormat:format,value];
} 

Answer 3

Old thread, I know, but this is a handy way to left pad. I have it my Util class. You can adapt it to right pad if needed. The best part is that it works with whatever padding you want.

+ (NSString *) leftPadString:(NSString *)s withPadding:(NSString *)padding {
    NSString *padded = [padding stringByAppendingString:s];
    return [padded substringFromIndex:[padded length] - [padding length]];
}

ARC and non-ARC compliant. :)

To call it, use [Util leftPadString:@"42" withPadding:@"0000"];.

You could also put it in a category on NSString for an even easier call like [@"42" stringByLeftPadding:@"0000"].

Both give you 0042.

Answer 4

This one pads left with 10 zeroes.

NSString *padded = [NSString stringWithFormat:@"Padded left with zeros: %010d", 65];

Answer 5

Clumsy, but it'll do the job.

@implementation NSString (LeftPadding)

- (NSString *)stringByPaddingTheLeftToLength:(NSUInteger)newLength withString:(NSString *)padString startingAtIndex:(NSUInteger)padIndex
{
    if ([self length] <= newLength)
        return [[@"" stringByPaddingToLength:newLength - [self length] withString:padString startingAtIndex:padIndex] stringByAppendingString:self];
    else
        return [[self copy] autorelease];
}

@end

Then you can do:

NSString *test1 = [@"6" stringByPaddingTheLeftToLength:10 withString:@"0" startingAtIndex:0];
// test1 = "0000000006"

NSString *test2 = [@"asdf" stringByPaddingTheLeftToLength:10 withString:@"qwer" startingAtIndex:0];
// test2 = "qwerqwasdf"

NSString *test3 = [@"More than ten characters" stringByPaddingTheLeftToLength:10 withString:@"bamboo" startingAtIndex:0];
// test3 = "More than ten characters"

NSString *test4 = [test3 stringByPaddingTheLeftToLength:100 withString:test2 startingAtIndex:0];
// test4 = "qwerqwasdfqwerqwasdfqwerqwasdf...qwerqMore than ten characters"