utf8OffsetToPointer
Converts from an integer character offset to a pointer to a position within the string.
Since 2.10, this function allows to pass a negative @offset to step backwards. It is usually worth stepping backwards from the end instead of forwards if @offset is in the last fourth of the string, since moving forward is about 3 times faster than moving backward.
Note that this function doesn't abort when reaching the end of @str. Therefore you should be sure that @offset is within string boundaries before calling that function. Call g_utf8_strlen() when unsure. This limitation exists as this function is called frequently during text rendering and therefore has to be as fast as possible.
Return
the resulting pointer
Parameters
a UTF-8 encoded string
a character offset within @str