[_kst_]

No, it merely assumes one byte per character. For example, it would work correctly in Latin-1 or EBCDIC.

In any case, the problem statement (though it's a bit vague) requires building a truncated string, not just printing it.

[pjmlp]

It is enough to have mixed 8 byte code pages and then it is worthless.

[kevin_thibedeau]

s/printf/sprintf/