How to determine whether a codec has a const ratio 'byte number per character'?

Question

Given an IANA codec name (or, one of those used in iconv/ICU), what is the easiest way to determine whether the codec has a fixed width representation for characters or not?

Answer 1

Use ucnv_isFixedWidth():

UErrorCode status;
UConverter* converter = ucnv_open("koi8-r", &status);
if (U_SUCCESS(status)) {
  UBool is_fixed = ucnv_isFixedWidth(converter, &status);
}