Converting a octal String to Decimal in Objective-C?

Question

I trying to do conversions between Binary, Octal, Decimal and Hexadecimal in Objective-C. I had problems converting Octal to Decimal.

I have tried the following:

NSString *decString = [NSString stringWithFormat:@"%d", 077];

It works fine, returning 63 as expected, but my Octal value is a NSString. How can I tell the computer that it is a Octal;

I know there is a method called "scanHexInt:" which I used to convert Hexadecimal to decimal, but it seems there is no scanOctInt...

Any help would be appreciated!

Answer 1

The cleanest solution is probably:

long result = strtol(input.UTF8String, NULL, 8);

or

long long result = strtoll(input.UTF8String, NULL, 8);

Answer 2

Define a category on NSString (put this on top of any of your source code modules or into a new .m/.h file pair, @interface goes into .h, @implementation into .m):

@interface NSString (NSStringWithOctal)
-(int)octalIntValue;
@end

@implementation NSString (NSStringWithOctal)
-(int)octalIntValue
{
    int iResult = 0, iBase = 1;
    char c;

    for(int i=(int)[self length]-1; i>=0; i--)
    {
        c = [self characterAtIndex:i];
        if((c<'0')||(c>'7')) return 0;
        iResult += (c - '0') * iBase;
        iBase *= 8; 
    }
    return iResult;
}
@end

Use it like that:

NSString *s = @"77";
int i = [s octalIntValue];
NSLog(@"%d", i);

The method returns an integer representing the octal value in the string. It returns 0, if the string is not an octal number. Leading zeroes are allowed, but not necessary.