gtk-text-buffer-iter-at-line-index (buffer line index)

buffer -- a gtk-text-buffer object
line -- an integer with the line number counting from 0
index -- an integer with the byte index from the start of the line

A gtk-text-iter iterator.

Obtains an iterator pointing to index within the given line. The index argument must be the start of a UTF-8 character. Note bytes, not characters, UTF-8 may encode one character as multiple bytes.

If the line argument is greater than the number of lines in the text buffer, the end iterator is returned. And if the index argument is off the end of the line, the iterator at the end of the line is returned.