stl_pair.h

stl_pair.h// Filename:    stl_pair.h// Comment By:  凝霜// E-mail:      [e-mail]// Blog:        http://blog.csdn.net/mdl13412/* * * Copyright (c) 1994 * Hewlett-Packard Company * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation.  Hewlett-Packard Company makes no * representations about the suitability of this software for any * purpose.  It is provided "as is" without express or implied warranty. * * * Copyright (c) 1996,1997 * Silicon Graphics Computer Systems, Inc. * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation.  Silicon Graphics makes no * representations about the suitability of this software for any * purpose.  It is provided "as is" without express or implied warranty. *//* NOTE: This is an internal header file, included by other STL headers. *   You should not attempt to use it directly. */#ifndef __SGI_STL_INTERNAL_PAIR_H#define __SGI_STL_INTERNAL_PAIR_H__STL_BEGIN_NAMESPACE// pair只是一个wraper, 所以要提供最佳效率// 使用struct的原因是我们要能方便的存取内部元素// pair在关联式容器中的使用极为广泛, 其本身也可以嵌套使用template <class T1, class T2>struct pair{  typedef T1 first_type;  typedef T2 second_type;  T1 first;  T2 second;  pair() : first(T1()), second(T2()) {}  pair(const T1& a, const T2& b) : first(a), second(b) {}  // 此版本并未提供operator =()的支持, 个人认为应该提供#ifdef __STL_MEMBER_TEMPLATES  // 允许使用兼容的pair进行复制构造  template <class U1, class U2>  pair(const pair<U1, U2>& p) : first(p.first), second(p.second) {}#endif};// 只有当pair中的两个成员均相等时, 才判定两个pair相等// 使用自定义类型时最好提供operator ==重载template <class T1, class T2>inline bool operator==(const pair<T1, T2>& x, const pair<T1, T2>& y){  return x.first == y.first && x.second == y.second;}// 连个pair进行比较操作时, 以第一个元素为主, 如果第一个元素不能决定表达式的值// 那么再进行第二个元素的比较// 使用自定义类型时最好提供operator <重载template <class T1, class T2>inline bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y){  return x.first < y.first || (!(y.first < x.first) && x.second < y.second);}// 至于为什么没有提供operator !=, >, >=, <=// 这个是因为其在<stl_relops.h>中有实现, 其只依赖operator <和==// 所以在此特化operator ==, <就能满足要求// 提供<stl_relops.h>的作用是如果需要特化operator XXX// 那么我们仅需要特化operator ==和<即可同时重载所有operator// 这里使用了RVO(Return Value Optimization)机制, 如果编译器支持,// 则可以消除临时对象的构造和析构负担// 详细细节见<Inside The C++ Object Model>template <class T1, class T2>inline pair<T1, T2> make_pair(const T1& x, const T2& y){  return pair<T1, T2>(x, y);}__STL_END_NAMESPACE#endif /* __SGI_STL_INTERNAL_PAIR_H */// Local Variables:// mode:C++// End: