Function bsetstr

int bsetstr (bstring b0, int pos, bstring b1, unsigned char fill) * * Overwrite the string b0 starting at position pos with the string b1. If * the position pos is past the end of b0, then the character "fill" is * appended as necessary to make up the gap between the end of b0 and pos. * If b1 is NULL, it behaves as if it were a 0-length string. */