Use the following tips:

• Working with a bytewise index into a string presents problems similar to those posed by pointer manipulation. Consider this example, which scans a string for a backslash character:

  while ( rgch[ i ] != '\\' )
      i++;

  This might index a trail byte, not a lead byte, and thus it might not point to a character.

• Use the _mbclen function to solve the preceding problem:

  while ( rgch[ i ] != '\\' )
      i += _mbclen ( rgch + i );

  This correctly indexes to a lead byte, hence to a character. The _mbclen function determines the size of a character (1 or 2 bytes).

MBCS Programming Tips
Last Character in a String