Re: NSString "midstring()"
Re: NSString "midstring()"
- Subject: Re: NSString "midstring()"
- From: Quincey Morris <email@hidden>
- Date: Sun, 17 Apr 2011 14:53:52 -0700
On Apr 17, 2011, at 14:08, JAMES ROGERS wrote:
> I have stepped this through with the debugger and no flags were raised. The code compiles without an error or a warning of any kind. I am afraid your response has overwhelmed me.
>
> One thing I will mention, I am not changing string. So that point is a moot one. I am just copying data out of the string.
>
> The "substring = [NSString stringWithUTF8String:sndBuffer]" was not my own and came from a website as a result of my query on "C string to NSString" and it works.
Sorry, didn't mean to be overwhelming. :)
Yes, the compiler is no help to you here. Testing might not show a problem either. If your text view happens to contain only ASCII characters (which are represented by a single element in both UTF-8 and UTF-16, and which fit in an 8-bit 'char'), you won't see a problem.
Here's how to change your code to avoid the 8-bit vs 16 bit and UTF-8 vs UTF-16 problem:
> unichar sndBuffer[65];
> int j;
>
> characterIndex++; // is always sitting at the last character sent so advance to the next character in string.
> for (j = 0; j < 65; j++) {
> sndBuffer[j] = [string characterAtIndex:characterIndex];
> characterIndex++;
> }
>
> substring = [NSString stringWithCharacters:sndBuffer length:j];
Or, more compactly as Mike suggested:
> int length = MIN ([string length] - characterIndex, 65);
> substring = [string substringWithRange: NSMakeRange (characterIndex, length)];
> characterIndex += length;
However, neither version solves the problem of breaking off in the middle of a multi-element UTF-16 sequence.
Incidentally, looking at your original code again, it sure looks like 'characterIndex' is getting over-incremented. You're going to skip over the first character of every substring. Shouldn't it be:
> unichar sndBuffer[65];
> int j;
>
> for (j = 0; j < 65; j++)
> sndBuffer[j] = [string characterAtIndex:++characterIndex]; // is always sitting at the last character sent so advance to the next character in string.
>
> substring = [NSString stringWithCharacters:sndBuffer length:j];
?
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