basic_string::find

size_type find(E c, size_type pos = 0) const;
size_type find(const E *s, size_type pos = 0) const;
size_type find(const E *s, size_type pos, size_type n) const;
size_type find(const basic_string& str, size_type pos = 0) const;

Each member function finds the first (lowest beginning position) subsequence in the controlled sequence, beginning on or after position pos, that matches the operand sequence specified by the remaining operands. If it succeeds, it returns the position where the matching subsequence begins. Otherwise, the function returns npos.