Count UTF8 chars in a line from a Local<String>

API reference: http://bespin.cz/~ondras/html/index.html

I need to count he number of chars in a line:

a b c d
e f g h

If I know that all the chars are ascii values then I can do:

Local<String> str = ...
String::AsciiValue s (str->ToString ());
unsigned char c;

for (int i=0; (c = (*s)[i]) != 0; i++){
  //...
}

But the string can contain characters encoded with more than 1 byte:

↓ ↓ a b
↓ a b c

I cannot convert the string to a char* because in this case ↓ is encoded in 3 bytes, one char per byte, so my algorithm will add 3 chars instead of 1.

So I need to get the substring. In javascrit is pretty simple:

var s = "↓ ↓ a b";
var c;
for (var i=0; i<s.length; i++){
  c = s.substring (i, i + 1);
  //or c= s[i];
}

I need to do the same in C++.

Local<String> str = ...

for (int i=0; i<str->Length (); i++){
  //???
  //Another alternative is to get the String of each position, something like this:
  //Local<String> s = str->Get (i);
}

Assuming that you are using this implementation of String::AsciiValue, there appears to be a length() method

Solved.

UTF8 code points: https://en.wikipedia.org/wiki/UTF-8

The basic idea is to mask the byte and check how many bytes must be ignored to fully read the multibyte char.

unsigned char masks[5] = { 192, 224, 240, 248, 252 };

Local<String> str = ...
String::Utf8Value s (str->ToString ());
unsigned char c;
int utf8Bytes = 0;

for (int i=0; (c = (*s)[i]) != 0; i++){
    //Ignore utf8 check for one byte chars
    if (c > 127){
        if (utf8Bytes){
            utf8Bytes--;
            continue;
        }

        //Check whether is a utf8 multibyte char
        for (int i=4; i>=0; i--){
            if ((c & r->masks[i]) == r->masks[i]){
                utf8Bytes = i + 1;
                break;
            }
        }

        if (utf8Bytes){
             //Do something if it's a multibyte char
        }

        continue;
    }

        //Do something to check lines, chars, etc
}