Trying to Understand NSString::initWithBytes

Question

I'm attempting conversion of a legacy C++ program to objective-C. The program needs an array of the 256 possible ASCII characters (8-bits per character). I'm attempting to use the NSString method initWithBytes:length:encoding: to do so. Unfortunately, when coded as shown below, it crashes (although it compiles).

NSString*     charasstring[256];
unsigned char char00;
int           temp00;
    for (temp00 = 0; temp00 <= 255; ++temp00)
        {
        char00 = (unsigned char)temp00;
        [charasstring[temp00] initWithBytes:&char00 length:1 encoding:NSASCIIStringEncoding]; 
        }

Please advise what I'm missing. Thank you.

Answer 1

First, the method is simply initWithBytes:length:encoding and not the NSString::initWithBytes you used in the title. I point this out only because forgetting everything you know from C++ is your first step towards success with Objective-C. ;)

Secondly, your code demonstrates that you don't understand Objective-C or use of the Foundation APIs.

• you aren't allocating instances of NSString anywhere

• you declared an array of 256 NSString instance pointers, probably not what you want

• a properly encoded ASCII string does not include all of the bytes

I would suggest you start here.

Answer 2

To solve that specific problem, the following code should do the trick:

NSMutableArray* ASCIIChars = [NSMutableArray arrayWithCapacity:256];
int i;
for (i = 0; i <= 255; ++i)
    {
    [ASCIIChars addObject:[NSString stringWithFormat:@"%c", (unsigned char)i]];
    }

To be used, later on, as follows:

NSString* oneChar = [ASCIIChars objectAtIndex:32]; // for example

However, if all you need is an array of characters, you can just use a simple C array of characters:

unsigned char ASCIIChars [256];
int i;
for (i = 0; i <= 255; ++i)
    {
    ASCIIChars[i] = (unsigned char)i;
    }

To be used, later on, as follows:

unsigned char c = ASCIIChars[32];

The choice will depend on how you want to use that array of characters.