basic_string::find_last_of

size_type find_last_of(E c, size_type pos = npos) const;
size_type find_last_of(const E *s, size_type pos = npos) const;
size_type find_last_of(const E *s, size_type pos, size_type n = npos) const;
size_type find_last_of(const basic_string& str,
    size_type pos = npos) const;

Each member function finds the last (highest position) element of the controlled sequence, at or before position pos, that matches any of the elements in the operand sequence specified by the remaining operands. If it succeeds, it returns the position. Otherwise, the function returns npos.