CODEWITHSUNDEEP
c++stringiterator
Martijn Courteaux
Martijn Courteaux

Reputation: 68907

C++: Char iteration over string (I'm getting crazy)

I have this string:

std::string str = "presents";

And when I iterate over the characters, they come in this order:

spresent

So, the last char comes first.

This is the code:

uint16_t c;
printf("%s: ", str.c_str());
for (unsigned int i = 0; i < str.size(); i += extractUTF8_Char(str, i, &c)) {
    printf("%c", c);
}
printf("\n");

And this is the exctract method:

uint8_t extractUTF8_Char(string line, int offset, uint16_t *target) {
 uint8_t ch = uint8_t(line.at(offset));
 if ((ch & 0xC0) == 0xC0) {
  if (!target) {
   return 2;
  }
  uint8_t ch2 = uint8_t(line.at(offset + 1));
  uint16_t fullCh = (uint16_t(((ch & 0x1F) >> 2)) << 8) | ((ch & 0x3) << 0x6) | (ch2 & 0x3F);
  *target = fullCh;
  return 2;
 }
 if (target) {
 *target = ch;
 }
 return 1;
}

This method returns the length of the character. So: 1 byte or 2 bytes. And if the length is 2 bytes, it extracts the UNICODE point out of the UTF8 string.

Upvotes: 1

Views: 1528

Answers (1)

lijie
lijie

Reputation: 4871

your first printf is printing nonsense (the initial value of c). The last c gotten is not printed.

This is because the call to extractUTF8_char is occurring in the last clause of the for statement. You might want to change it to

for (unsigned int i = 0; i < str.size();) {
    i += extractUTF8_Char(str, i, &c);
    printf("%c", c);
}

instead.

Upvotes: 17

Related Questions