Return the character index of the byte at {idx} in {string}. The index of the first character is zero. If there are no multibyte characters the returned value is equal to {idx}. When {countcc} is omitted or FALSE, then composing characters are not counted separately, their byte length is added to the preceding base character. When {countcc} is TRUE, then composing characters are counted as separate characters. Returns -1 if the arguments are invalid or if {idx} is greater than the index of the last byte in {string}. An error is given if the first argument is not a string, the second argument is not a number or when the third argument is present and is not zero or one. See byteidx() and byteidxcomp() for getting the byte index from the character index. Examples:

echo charidx('áb́ć', 3)               returns 1
echo charidx('áb́ć', 6, 1)    returns 4
echo charidx('áb́ć', 16)              returns -1

Can also be used as a method:

GetName()->charidx(idx)