STL源码剖析之算法：lexicograhpical_compare

template <class InputIterator1, class InputIterator2, class Compare>              
bool Lexicographical_compare(InputIterator1 first1, InputIterator1 last1,         
                             InputIterator2 first2, InputIterator2 last2,         
                             Compare comp) {                                      
    for(; first1 != last1 && first2 != last2; ++first1, ++first2) {               
        if(comp(*first1, *first2))                                                
            return true;                                                          
        if(comp(*first2, *first1))                                                
            return false;                                                         
    }                                                                             
    return first1 == last1 && first2 != last2;                                    
} 

     效率至上的SGI还设计了一个特化版本，针对原生指针 const unsigned char*：

inline bool lexicographical_compare(const unsigned char* first1, 
                              const unsigned char* last1, 
                              const unsigned char* first2, 
                              const unsigned char* last2) { 
    const size_t len1 = last1 - first1; 
    const size_t len2 = last2 - first2; 
    const int result = memcmp(first1, first2, min(len1, len2)); 
    return result != 0 ? result < 0 : len1 < len2; 
}