equal 源码剖析

一：功能解析

函数原型：

equality (1)
template <class InputIterator1, class InputIterator2>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2);
predicate (2)
template <class InputIterator1, class InputIterator2, class BinaryPredicate>
bool equal (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, BinaryPredicate pred);

功能：

区间[ first1 , last1 )与以first2开始的区间逐一比较，如果与[ first1 , last1 )全部相等（或者满足pred），返回布尔值真，否则返回假。

例子：

// equal algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::equal
#include <vector>       // std::vectorbool mypredicate (int i, int j) {return (i==j);
}int main () {int myints[] = {20,40,60,80,100};               //   myints: 20 40 60 80 100std::vector<int>myvector (myints,myints+5);     // myvector: 20 40 60 80 100// using default comparison:if ( std::equal (myvector.begin(), myvector.end(), myints) )std::cout << "The contents of both sequences are equal.\n";elsestd::cout << "The contents of both sequences differ.\n";myvector[3]=81;                                 // myvector: 20 40 60 81 100// using predicate comparison:if ( std::equal (myvector.begin(), myvector.end(), myints, mypredicate) )std::cout << "The contents of both sequences are equal.\n";elsestd::cout << "The contents of both sequences differ.\n";return 0;
}

运行如下：

The contents of both sequences are equal.
The contents of both sequence differ.

二：源码剖析

// TEMPLATE FUNCTION equal WITH PRED
template<class _InIt1,class _InIt2,class _Pr> inlinebool _Equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _Pr _Pred){   // compare [_First1, _Last1) to [_First2, ...) using _Predfor (; _First1 != _Last1; ++_First1, (void)++_First2)if (!_Pred(*_First1, *_First2))return (false);return (true);}inline bool _Equal(const char *_First1, const char *_Last1,const char *_First2, equal_to<>){   // compare [_First1, _Last1) to [_First2, ...), for charsreturn (_CSTD memcmp(_First1, _First2, _Last1 - _First1) == 0);}inline bool _Equal(const signed char *_First1, const signed char *_Last1,const signed char *_First2, equal_to<>){   // compare [_First1, _Last1) to [_First2, ...), for signed charsreturn (_CSTD memcmp(_First1, _First2, _Last1 - _First1) == 0);}inline bool _Equal(const unsigned char *_First1, const unsigned char *_Last1,const unsigned char *_First2, equal_to<>){   // compare [_First1, _Last1) to [_First2, ...), for unsigned charsreturn (_CSTD memcmp(_First1, _First2, _Last1 - _First1) == 0);}inline bool _Equal(const char *_First1, const char *_Last1,const char *_First2, _Char_traits_eq<char_traits<char>>){   // compare [_First1, _Last1) to [_First2, ...), for charsreturn (_CSTD memcmp(_First1, _First2, _Last1 - _First1) == 0);}#if _ITERATOR_DEBUG_LEVEL == 0
template<class _InIt1,class _InIt2,class _Pr> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _Pr _Pred){   // compare [_First1, _Last1) to [_First2, ...) using _Predreturn (_Equal(_Unchecked(_First1), _Unchecked(_Last1),_Unchecked(_First2), _Pred));}#else /* _ITERATOR_DEBUG_LEVEL == 0 */
template<class _InIt1,class _InIt2,class _Pr> inlinebool _Equal2(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _Pr _Pred, true_type){   // compare [_First1, _Last1) to [_First2, ...) using _Pred, checkedreturn (_Equal(_First1, _Last1,_First2, _Pred));}template<class _InIt1,class _InIt2,class _Pr> inline
_SCL_INSECURE_DEPRECATEbool _Equal2(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _Pr _Pred, false_type){   // compare [_First1, _Last1) to [_First2, ...) using _Pred, uncheckedreturn (_Equal(_First1, _Last1,_First2, _Pred));}template<class _InIt1,class _InIt2,class _Pr> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _Pr _Pred){   // compare [_First1, _Last1) to [_First2, ...) using _Pred_DEBUG_RANGE_PTR(_First1, _Last1, _First2);_DEBUG_POINTER_IF(_First1 != _Last1, _Pred);return (_Equal2(_Unchecked(_First1), _Unchecked(_Last1),_First2, _Pred, _Is_checked(_First2)));}#if _ITERATOR_DEBUG_ARRAY_OVERLOADS
template<class _InIt1,class _InTy,size_t _InSize,class _Pr> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InTy (&_First2)[_InSize], _Pr _Pred){   // compare [_First1, _Last1) to [_First2, ...) using _Predreturn (_STD equal(_First1, _Last1,_Array_iterator<_InTy, _InSize>(_First2), _Pred));}#endif /* _ITERATOR_DEBUG_ARRAY_OVERLOADS */#endif /* _ITERATOR_DEBUG_LEVEL == 0 */// TEMPLATE FUNCTION equal
template<class _InIt1,class _InIt2> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2){   // compare [_First1, _Last1) to [_First2, ...)return (_STD equal(_First1, _Last1, _First2,equal_to<>()));}#if _ITERATOR_DEBUG_ARRAY_OVERLOADS
template<class _InIt1,class _InTy,size_t _InSize> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InTy (&_First2)[_InSize]){   // compare [_First1, _Last1) to [_First2, ...)return (_STD equal(_First1, _Last1, _First2,equal_to<>()));}#endif /* _ITERATOR_DEBUG_ARRAY_OVERLOADS */// TEMPLATE FUNCTION equal WITH TWO RANGES, PRED
template<class _InIt1,class _InIt2,class _Pr> inlinebool _Equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _InIt2 _Last2, _Pr _Pred,input_iterator_tag, input_iterator_tag){   // compare [_First1, _Last1) to [_First2, _Last2)// using _Pred, arbitrary iterators_DEBUG_POINTER_IF(_First1 != _Last1 && _First2 != _Last2, _Pred);for (; _First1 != _Last1 && _First2 != _Last2; ++_First1, (void)++_First2)if (!_Pred(*_First1, *_First2))return (false);return (_First1 == _Last1 && _First2 == _Last2);}template<class _InIt1,class _InIt2,class _Pr> inlinebool _Equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _InIt2 _Last2, _Pr _Pred,random_access_iterator_tag, random_access_iterator_tag){   // compare [_First1, _Last1) to [_First2, _Last2)// using _Pred, random-access iteratorsif (_Last1 - _First1 != _Last2 - _First2)return (false);_DEBUG_POINTER_IF(_First1 != _Last1, _Pred);return (_Equal(_First1, _Last1, _First2, _Pred));}template<class _InIt1,class _InIt2,class _Pr> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _InIt2 _Last2, _Pr _Pred){   // compare [_First1, _Last1) to [_First2, _Last2) using _Pred_DEBUG_RANGE(_First1, _Last1);_DEBUG_RANGE(_First2, _Last2);return (_Equal(_Unchecked(_First1), _Unchecked(_Last1),_Unchecked(_First2), _Unchecked(_Last2), _Pred,_Iter_cat(_First1), _Iter_cat(_First2)));}// TEMPLATE FUNCTION equal WITH TWO RANGES
template<class _InIt1,class _InIt2> inlinebool equal(_InIt1 _First1, _InIt1 _Last1,_InIt2 _First2, _InIt2 _Last2){   // compare [_First1, _Last1) to [_First2, _Last2)return (_STD equal(_First1, _Last1, _First2, _Last2,equal_to<>()));}

源码摘抄自Visual Studio 2015安装目录algorithm文件中。

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