Question

I have implemented some code to convert a NSString of “text” to an NSString of (ASCII) ints, like so:

@"Hello" is converted to @"72 101 108 108 111"

However, I am having quite a bit of difficulty doing the opposite. Starting with a string of ints (with the spaces) and converting back to the plain string of text.

What I need: @"72 101 108 108 111" must be converted to @"Hello"

I have tried breaking up the input string into an int array, iterating through it, and using repeatedly the following:

[NSString stringWithFormat:@"%c", decCharArray[i]]

However, the problem with that is that it parses each particular digit into ASCII, converting the 7, the 2, the space, the 1, etc.

Thanks a ton in advance.

Answer 1

There is no real magic on it. Since you’ll be using ASCII, to convert an int
to a char all you have to do is an assignment, as you may already know:

char a = 65; /* a contains 'A' */

NSString has a very convenient method componentsSeparatedByString: that will
return an array of strings containing your numbers, and you can get an int
from a string with the intValue method. Thus, all you have to do is to split
the string and iterate through the components assigning their int value to a
char array. Here is an example function that does that:

NSString *
TextFromAsciiCodesString (NSString *string)
{
    NSArray *components = [string componentsSeparatedByString:@" "];
    NSUInteger len = [components count];
    char new_str[len+1];

    int i;
    for (i = 0; i < len; ++i)
        new_str[i] = [[components objectAtIndex:i] intValue];

    new_str[i] = '\0';

    return [NSString stringWithCString:new_str
                              encoding:NSASCIIStringEncoding];
}

And a simple use of it, with your "Hello" example:

NSString *string = @"72 101 108 108 111";
NSLog(@"%@", TextFromAsciiCodesString(string));

Actually, it’s a bit different as your example was "Hell^K" 🙂