STL源码剖析——STL算法之find查找算法
前言
由于在前文的《STL算法剖析》中，源码剖析非常多，不方便学习，也不方便以后复习，这里把这些算法进行归类，对他们单独的源码剖析进行讲解。本文介绍的STL算法中的find、search查找算法。在STL源码中有关算法的函数大部分在本文介绍，包含findand find_if、adjacent_find、search、search_n、lower_bound、 upper_bound、 equal_range、binary_search、find_first_of、find_end相关算法，下面对这些算法的源码进行了详细的剖析，并且适当给出应用例子，增加我们对其理解，方便我们使用这些算法。具体详见下面源码剖析。
查找算法源码剖析
// find and find_if.
//查找区间[first,last)内元素第一个与value值相等的元素，并返回其位置
//其中find函数是采用默认的equality操作operator==
//find_if是采用用户自行指定的操作pred
//若find函数萃取出来的迭代器类型为输入迭代器input_iterator_tag，则调用此函数
template
inline _InputIter find(_InputIter __first, _InputIter __last,
const _Tp& __val,
input_iterator_tag)
{//若尚未到达区间的尾端，且未找到匹配的值，则继续查找
while (__first != __last && !(*__first == __val))
++__first;
//若找到匹配的值，则返回该位置
//若找不到，即到达区间尾端，此时first=last，则返回first
return __first;
}
//若find_if函数萃取出来的迭代器类型为输入迭代器input_iterator_tag，则调用此函数
template
inline _InputIter find_if(_InputIter __first, _InputIter __last,
_Predicate __pred,
input_iterator_tag)
{//若尚未到达区间的尾端，且未找到匹配的值，则继续查找
while (__first != __last && !__pred(*__first))
++__first;
//若找到匹配的值，则返回该位置
//若找不到，即到达区间尾端，此时first=last，则返回first
return __first;
}
#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
//若find函数萃取出来的迭代器类型为随机访问迭代器random_access_iterator_tag，则调用此函数
template
_RandomAccessIter find(_RandomAccessIter __first, _RandomAccessIter __last,
const _Tp& __val,
random_access_iterator_tag)
{
typename iterator_traits<_RandomAccessIter>::difference_type __trip_count
= (__last - __first) >> 2;
for ( ; __trip_count > 0 ; --__trip_count) {
if (*__first == __val) return __first;
++__first;
if (*__first == __val) return __first;
++__first;
if (*__first == __val) return __first;
++__first;
if (*__first == __val) return __first;
++__first;
}
switch(__last - __first) {
case 3:
if (*__first == __val) return __first;
++__first;
case 2:
if (*__first == __val) return __first;
++__first;
case 1:
if (*__first == __val) return __first;
++__first;
case 0:
default:
return __last;
}
}
//若find_if函数萃取出来的迭代器类型为随机访问迭代器random_access_iterator_tag，则调用此函数
template
_RandomAccessIter find_if(_RandomAccessIter __first, _RandomAccessIter __last,
_Predicate __pred,
random_access_iterator_tag)
{
typename iterator_traits<_RandomAccessIter>::difference_type __trip_count
= (__last - __first) >> 2;
for ( ; __trip_count > 0 ; --__trip_count) {
if (__pred(*__first)) return __first;
++__first;
if (__pred(*__first)) return __first;
++__first;
if (__pred(*__first)) return __first;
++__first;
if (__pred(*__first)) return __first;
++__first;
}
switch(__last - __first) {
case 3:
if (__pred(*__first)) return __first;
++__first;
case 2:
if (__pred(*__first)) return __first;
++__first;
case 1:
if (__pred(*__first)) return __first;
++__first;
case 0:
default:
return __last;
}
}
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
/*find函数功能：Returns an iterator to the first element in the range [first,last) that compares equal to val.
If no such element is found, the function returns last.
find函数原型：
template
InputIterator find (InputIterator first, InputIterator last, const T& val);
*/
//find函数对外接口
template
inline _InputIter find(_InputIter __first, _InputIter __last,
const _Tp& __val)
{
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool,
typename iterator_traits<_InputIter>::value_type, _Tp);
//首先萃取出first迭代器的类型，根据迭代器的类型调用不同的函数
return find(__first, __last, __val, __ITERATOR_CATEGORY(__first));
}
/*find_if函数功能：Returns an iterator to the first element in the range [first,last) for which pred returns true.
If no such element is found, the function returns last.
find_if函数原型：
template
InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);
*/
//find_if 函数对外接口
template
inline _InputIter find_if(_InputIter __first, _InputIter __last,
_Predicate __pred) {
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_UNARY_FUNCTION_CHECK(_Predicate, bool,
typename iterator_traits<_InputIter>::value_type);
//首先萃取出first迭代器的类型，根据迭代器的类型调用不同的函数
return find_if(__first, __last, __pred, __ITERATOR_CATEGORY(__first));
}
//find和find_if函数举例：
/*
#include // std::cout
#include // std::find_if
#include // std::vector
bool IsOdd (int i) {
return ((i%2)==1);
}
int main () {
std::vector myvector;
myvector.push_back(10);
myvector.push_back(25);
myvector.push_back(40);
myvector.push_back(55);
std::vector::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);
std::cout << "The first odd value is " << *it << '\n';
// using std::find with vector and iterator:
it = find (myvector.begin(), myvector.end(), 40);
if (it != myvector.end())
std::cout << "Element found in myvector: " << *it << '\n';
else
std::cout << "Element not found in myints\n";
return 0;
}
Output:
The first odd value is 25
Element found in myvector: 40
*/
// adjacent_find.
//查找区间[first,last)内第一次重复的相邻元素
//若存在返回相邻元素的第一个元素位置
//若不存在返回last位置
/*该函数有两个版本：第一版本是默认操作operator==；第二版本是用户指定的二元操作pred
函数对外接口的原型：
equality (1)：默认操作是operator==
template
ForwardIterator adjacent_find (ForwardIterator first, ForwardIterator last);
predicate (2)：用户指定的二元操作pred
template
ForwardIterator adjacent_find (ForwardIterator first, ForwardIterator last,
BinaryPredicate pred);
*/
//版本一：默认操作是operator==
template
_ForwardIter adjacent_find(_ForwardIter __first, _ForwardIter __last) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES(typename iterator_traits<_ForwardIter>::value_type,
_EqualityComparable);
/*
情况1：若输入区间为空，则直接返回尾端last；
情况2：若输入区间不为空，且存在相邻重复元素，则返回相邻元素的第一个元素的位置；
情况3：若输入区间不为空，但是不存在相邻重复元素，则直接返回尾端last；
*/
//情况1：
if (__first == __last)//若输入区间为空
return __last;//直接返回last
//情况2：
_ForwardIter __next = __first;//定义当前位置的下一个位置(即当前元素的相邻元素)
while(++__next != __last) {//若还没到达尾端，执行while循环
if (*__first == *__next)//相邻元素值相等，则找到相邻重复元素
return __first;//返回第一个元素的位置
__first = __next;//若暂时找不到，则继续找，直到到达区间尾端
}
//情况3：
return __last;//直接返回尾端last
}
//版本二：用户指定的二元操作pred
//实现过程和版本一一样，只是判断规则不同
template
_ForwardIter adjacent_find(_ForwardIter __first, _ForwardIter __last,
_BinaryPredicate __binary_pred) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool,
typename iterator_traits<_ForwardIter>::value_type,
typename iterator_traits<_ForwardIter>::value_type);
if (__first == __last)
return __last;
_ForwardIter __next = __first;
while(++__next != __last) {
//如果找到相邻元素符合用户指定条件，就返回第一元素位置
if (__binary_pred(*__first, *__next))
return __first;
__first = __next;
}
return __last;
}
//adjacent_find函数举例：
/*
#include // std::cout
#include // std::adjacent_find
#include // std::vector
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {5,20,5,30,30,20,10,10,20};
std::vector myvector (myints,myints+8);
std::vector::iterator it;
// using default comparison:
it = std::adjacent_find (myvector.begin(), myvector.end());
if (it!=myvector.end())
std::cout << "the first pair of repeated elements are: " << *it << '\n';
//using predicate comparison:
it = std::adjacent_find (++it, myvector.end(), myfunction);
if (it!=myvector.end())
std::cout << "the second pair of repeated elements are: " << *it << '\n';
return 0;
}
Output:
the first pair of repeated elements are: 30
the second pair of repeated elements are: 10
*/
// search.
//在序列一[first1,last1)所涵盖的区间中，查找序列二[first2,last2)的首次出现点
//该查找函数有两个版本：
//版本一：使用默认的equality操作operator==
//版本二：用户根据需要自行指定操作规则
/*search函数功能：Searches the range [first1,last1) for the first occurrence of the sequence defined by [first2,last2),
and returns an iterator to its first element, or last1 if no occurrences are found.
search函数的原型：
equality (1)：版本一
template
ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
predicate (2)：版本二
template
ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
*/
//版本一：使用默认的equality操作operator==
template
_ForwardIter1 search(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2)
{
__STL_REQUIRES(_ForwardIter1, _ForwardIterator);
__STL_REQUIRES(_ForwardIter2, _ForwardIterator);
__STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool,
typename iterator_traits<_ForwardIter1>::value_type,
typename iterator_traits<_ForwardIter2>::value_type);
// Test for empty ranges
if (__first1 == __last1 || __first2 == __last2)
return __first1;
// Test for a pattern of length 1.
_ForwardIter2 __tmp(__first2);
++__tmp;
if (__tmp == __last2)
return find(__first1, __last1, *__first2);
// General case.
_ForwardIter2 __p1, __p;
__p1 = __first2; ++__p1;
_ForwardIter1 __current = __first1;
while (__first1 != __last1) {//若还没到达区间尾端
__first1 = find(__first1, __last1, *__first2);//查找*first2在区间[first1,last1)首次出现的位置
if (__first1 == __last1)//若在[first1,last1)中不存在*first2，即在[first1,last1)不存在子序列[first2,last2)
return __last1;//则直接返回区间尾端
__p = __p1;
__current = __first1;
if (++__current == __last1)//若[first1,last1)只有一个元素，即序列[first1,last1)小于序列[first2,last2)
return __last1;//不可能成为其子序列，返回last1
while (*__current == *__p) {//若两个序列相对应的值相同
if (++__p == __last2)//若序列[first2,last2)只有两个元素，且与序列一匹配
return __first1;//则返回匹配的首次位置
if (++__current == __last1)//若第一个序列小于第二个序列
return __last1;//返回last1
}
++__first1;
}
return __first1;
}
//版本二：用户根据需要自行指定操作规则
template
_ForwardIter1 search(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2,
_BinaryPred __predicate)
{
__STL_REQUIRES(_ForwardIter1, _ForwardIterator);
__STL_REQUIRES(_ForwardIter2, _ForwardIterator);
__STL_BINARY_FUNCTION_CHECK(_BinaryPred, bool,
typename iterator_traits<_ForwardIter1>::value_type,
typename iterator_traits<_ForwardIter2>::value_type);
// Test for empty ranges
if (__first1 == __last1 || __first2 == __last2)
return __first1;
// Test for a pattern of length 1.
_ForwardIter2 __tmp(__first2);
++__tmp;
if (__tmp == __last2) {
while (__first1 != __last1 && !__predicate(*__first1, *__first2))
++__first1;
return __first1;
}
// General case.
_ForwardIter2 __p1, __p;
__p1 = __first2; ++__p1;
_ForwardIter1 __current = __first1;
while (__first1 != __last1) {
while (__first1 != __last1) {
if (__predicate(*__first1, *__first2))
break;
++__first1;
}
while (__first1 != __last1 && !__predicate(*__first1, *__first2))
++__first1;
if (__first1 == __last1)
return __last1;
__p = __p1;
__current = __first1;
if (++__current == __last1) return __last1;
while (__predicate(*__current, *__p)) {
if (++__p == __last2)
return __first1;
if (++__current == __last1)
return __last1;
}
++__first1;
}
return __first1;
}
// search_n. Search for __count consecutive copies of __val.
//在序列[first,last)查找连续count个符合条件值value元素的位置
//该查找函数有两个版本：
//版本一：使用默认的equality操作operator==
//版本二：用户根据需要自行指定操作规则
/*search_n函数功能：Searches the range [first,last) for a sequence of count elements,
each comparing equal to val (or for which pred returns true).
search_n函数的原型：
equality (1)：版本一
template
ForwardIterator search_n (ForwardIterator first, ForwardIterator last,
Size count, const T& val);
predicate (2)：版本二
template
ForwardIterator search_n ( ForwardIterator first, ForwardIterator last,
Size count, const T& val, BinaryPredicate pred );
*/
//版本一：使用默认的equality操作operator==
template
_ForwardIter search_n(_ForwardIter __first, _ForwardIter __last,
_Integer __count, const _Tp& __val) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES(typename iterator_traits<_ForwardIter>::value_type,
_EqualityComparable);
__STL_REQUIRES(_Tp, _EqualityComparable);
if (__count <= 0)
return __first;
else {//首先查找value第一次出现的位置
__first = find(__first, __last, __val);
while (__first != __last) {//若出现的位置不是区间尾端
_Integer __n = __count - 1;//更新个数，下面只需查找n=count-1个连续相同value即可
_ForwardIter __i = __first;
++__i;//从当前位置的下一个位置开始查找
//若没有到达区间尾端，且个数n大于0，且区间元素与value值相等
while (__i != __last && __n != 0 && *__i == __val) {
++__i;//继续查找
--__n;//减少查找的次数，因为已经找到value再次出现
}
if (__n == 0)//若区间尚未到达尾端，但是count个value已经查找到
return __first;//则输出查找到的首次出现value的位置
else
__first = find(__i, __last, __val);//若尚未找到连续count个value值的位置，则找出value下次出现的位置，并准备下一次while循环
}
return __last;
}
}
//版本二：用户根据需要自行指定操作规则
template
_ForwardIter search_n(_ForwardIter __first, _ForwardIter __last,
_Integer __count, const _Tp& __val,
_BinaryPred __binary_pred) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_BINARY_FUNCTION_CHECK(_BinaryPred, bool,
typename iterator_traits<_ForwardIter>::value_type, _Tp);
if (__count <= 0)
return __first;
else {
while (__first != __last) {
if (__binary_pred(*__first, __val))
break;
++__first;
}
while (__first != __last) {
_Integer __n = __count - 1;
_ForwardIter __i = __first;
++__i;
while (__i != __last && __n != 0 && __binary_pred(*__i, __val)) {
++__i;
--__n;
}
if (__n == 0)
return __first;
else {
while (__i != __last) {
if (__binary_pred(*__i, __val))
break;
++__i;
}
__first = __i;
}
}
return __last;
}
}
//search和search_n函数举例：
/*
#include // std::cout
#include // std::search_n
#include // std::vector
bool mypredicate (int i, int j) {
return (i==j);
}
int main () {
int myints[]={10,20,30,30,20,10,10,20};
std::vector myvector (myints,myints+8);
std::vector::iterator it;
// using default comparison:
it = std::search_n (myvector.begin(), myvector.end(), 2, 30);
if (it!=myvector.end())
std::cout << "two 30s found at position " << (it-myvector.begin()) << '\n';
else
std::cout << "match not found\n";
// using predicate comparison:
it = std::search_n (myvector.begin(), myvector.end(), 2, 10, mypredicate);
if (it!=myvector.end())
std::cout << "two 10s found at position " << int(it-myvector.begin()) << '\n';
else
std::cout << "match not found\n";
int needle1[] = {10,20};
// using default comparison:
it = std::search (myvector.begin(), myvector.end(), needle1, needle1+2);
if (it!=myvector.end())
std::cout << "needle1 found at position " << (it-myvector.begin()) << '\n';
else
std::cout << "needle1 not found\n";
// using predicate comparison:
int needle2[] = {30,20,10};
it = std::search (myvector.begin(), myvector.end(), needle2, needle2+3, mypredicate);
if (it!=myvector.end())
std::cout << "needle2 found at position " << (it-myvector.begin()) << '\n';
else
std::cout << "needle2 not found\n";
return 0;
}
Output:
two 30s found at position 2
two 10s found at position 5
needle1 found at position 0
needle2 found at position 3
*/
// Binary search (lower_bound, upper_bound, equal_range, binary_search).
template
_ForwardIter __lower_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);//求取整个区间的长度len
_Distance __half;
_ForwardIter __middle;//定义区间的中间迭代器
while (__len > 0) {//若区间不为空，则在区间[first,last)开始查找value值
__half = __len >> 1;//向右移一位，相当于除以2，即取区间的中间值
__middle = __first;//middle初始化为区间的起始位置
advance(__middle, __half);//middle向后移half位，此时middle为区间的中间值
if (*__middle < __val) {//将value值与中间值比较，即是二分查找,若中间值小于value，则继续查找右半部分
//下面两行令first指向middle的下一个位置
__first = __middle;
++__first;
__len = __len - __half - 1;//调整查找区间的长度
}
else
__len = __half;//否则查找左半部分
}
return __first;
}
//在已排序区间[first,last)查找value值
//若该区间存在与value相等的元素，则返回指向第一个与value相等的迭代器
//若该区间不存在与value相等的元素，则返回指向第一个不小于value值的迭代器
//若该区间的任何元素都比value值小，则返回last
/*
函数功能：Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val.
函数原型：
default (1) ：版本一采用operator<比较
template
ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last,
const T& val);
custom (2) ：版本二采用仿函数comp比较规则
template
ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last,
const T& val, Compare comp);
*/
//版本一
template
inline _ForwardIter lower_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_REQUIRES(_Tp, _LessThanComparable);
return __lower_bound(__first, __last, __val,
__DISTANCE_TYPE(__first));
}
template
_ForwardIter __lower_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Compare __comp, _Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);//求取整个区间的长度len
_Distance __half;
_ForwardIter __middle;//定义区间的中间迭代器
while (__len > 0) {//若区间不为空，则在区间[first,last)开始查找value值
__half = __len >> 1;//向右移一位，相当于除以2，即取区间的中间值
__middle = __first;//middle初始化为区间的起始位置
advance(__middle, __half);//middle向后移half位，此时middle为区间的中间值
if (__comp(*__middle, __val)) {//若comp判断为true，则继续在右半部分查找
//下面两行令first指向middle的下一个位置
__first = __middle;
++__first;
__len = __len - __half - 1;//调整查找区间的长度
}
else
__len = __half;//否则查找左半部分
}
return __first;
}
//版本二：
template
inline _ForwardIter lower_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Compare __comp) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp);
return __lower_bound(__first, __last, __val, __comp,
__DISTANCE_TYPE(__first));
}
template
_ForwardIter __upper_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);//求取整个区间的长度len
_Distance __half;
_ForwardIter __middle;//定义区间的中间迭代器
while (__len > 0) {//若区间不为空，则在区间[first,last)开始查找value值
__half = __len >> 1;//向右移一位，相当于除以2，即取区间的中间值
__middle = __first;//middle初始化为区间的起始位置
advance(__middle, __half);//middle向后移half位，此时middle为区间的中间值
if (__val < *__middle)//若value小于中间元素值
__len = __half;//查找左半部分
else {
//下面两行令first指向middle的下一个位置
__first = __middle;
++__first;
__len = __len - __half - 1;//更新len的值
}
}
return __first;
}
//在已排序区间[first,last)查找value值
//返回大于value值的第一个元素的迭代器
/*
函数功能：Returns an iterator pointing to the first element in the range [first,last) which compares greater than val.
函数原型：
default (1) ：版本一采用operator<比较
template
ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last,
const T& val);
custom (2) ：版本二采用仿函数comp比较规则
template
ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last,
const T& val, Compare comp);
*/
//版本一
template
inline _ForwardIter upper_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_REQUIRES(_Tp, _LessThanComparable);
return __upper_bound(__first, __last, __val,
__DISTANCE_TYPE(__first));
}
template
_ForwardIter __upper_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Compare __comp, _Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);
_Distance __half;
_ForwardIter __middle;
while (__len > 0) {
__half = __len >> 1;
__middle = __first;
advance(__middle, __half);
if (__comp(__val, *__middle))
__len = __half;
else {
__first = __middle;
++__first;
__len = __len - __half - 1;
}
}
return __first;
}
//版本二
template
inline _ForwardIter upper_bound(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val, _Compare __comp) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp);
return __upper_bound(__first, __last, __val, __comp,
__DISTANCE_TYPE(__first));
}
//函数举例
/*
#include // std::cout
#include // std::lower_bound, std::upper_bound, std::sort
#include // std::vector
int main () {
int myints[] = {10,20,30,30,20,10,10,20};
std::vector v(myints,myints+8); // 10 20 30 30 20 10 10 20
std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30
std::vector::iterator low,up;
low=std::lower_bound (v.begin(), v.end(), 20); // ^
up= std::upper_bound (v.begin(), v.end(), 20); // ^
std::cout << "lower_bound at position " << (low- v.begin()) << '\n';
std::cout << "upper_bound at position " << (up - v.begin()) << '\n';
return 0;
}
Output:
lower_bound at position 3
upper_bound at position 6
*/
template
pair<_ForwardIter, _ForwardIter>
__equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val,
_Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);//计算区间的长度len
_Distance __half;
_ForwardIter __middle, __left, __right;
while (__len > 0) {//若区间非空
__half = __len >> 1;//len右移一位，相等于除以2，即half为区间的长度的一半
__middle = __first;//初始化middle的值
advance(__middle, __half);//前进middle位置，使其指向区间中间位置
if (*__middle < __val) {//若指定元素value大于中间元素值，则在右半部分继续查找
//下面两行使first指向middle的下一个位置，即右半区间的起始位置
__first = __middle;
++__first;
__len = __len - __half - 1;//更新待查找区间的长度
}
else if (__val < *__middle)//若指定元素value小于中间元素值，则在左半部分继续查找
__len = __half;//更新待查找区间的长度
else {//若指定元素value等于中间元素值
//在前半部分找lower_bound位置
__left = lower_bound(__first, __middle, __val);
advance(__first, __len);
//在后半部分找upper_bound
__right = upper_bound(++__middle, __first, __val);
return pair<_ForwardIter, _ForwardIter>(__left, __right);//返回pair对象，第一个迭代器为left，第二个迭代器为right
}
}
return pair<_ForwardIter, _ForwardIter>(__first, __first);
}
//查找区间与value相等的相邻重复元素的起始位置和结束位置
//注意：[first,last)是已排序，思想还是采用二分查找法
//同样也有两个版本
/*
函数功能：Returns the bounds of the subrange that includes all the elements of the range [first,last) with values equivalent to val.
函数原型：
default (1) ：版本一默认operator<
template
pair
equal_range (ForwardIterator first, ForwardIterator last, const T& val);
custom (2) ：版本二采用仿函数comp
template
pair
equal_range (ForwardIterator first, ForwardIterator last, const T& val,
Compare comp);
*/
//版本一
template
inline pair<_ForwardIter, _ForwardIter>
equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_REQUIRES(_Tp, _LessThanComparable);
return __equal_range(__first, __last, __val,
__DISTANCE_TYPE(__first));
}
template
pair<_ForwardIter, _ForwardIter>
__equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val,
_Compare __comp, _Distance*)
{
_Distance __len = 0;
distance(__first, __last, __len);
_Distance __half;
_ForwardIter __middle, __left, __right;
while (__len > 0) {
__half = __len >> 1;
__middle = __first;
advance(__middle, __half);
if (__comp(*__middle, __val)) {
__first = __middle;
++__first;
__len = __len - __half - 1;
}
else if (__comp(__val, *__middle))
__len = __half;
else {
__left = lower_bound(__first, __middle, __val, __comp);
advance(__first, __len);
__right = upper_bound(++__middle, __first, __val, __comp);
return pair<_ForwardIter, _ForwardIter>(__left, __right);
}
}
return pair<_ForwardIter, _ForwardIter>(__first, __first);
}
//版本二
template
inline pair<_ForwardIter, _ForwardIter>
equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val,
_Compare __comp) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp);
return __equal_range(__first, __last, __val, __comp,
__DISTANCE_TYPE(__first));
}
//equal_range函数举例：
/*
#include // std::cout
#include // std::equal_range, std::sort
#include // std::vector
bool mygreater (int i,int j) { return (i>j); }
int main () {
int myints[] = {10,20,30,30,20,10,10,20};
std::vector v(myints,myints+8); // 10 20 30 30 20 10 10 20
std::pair::iterator,std::vector::iterator> bounds;
// using default comparison:
std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30
bounds=std::equal_range (v.begin(), v.end(), 20); // ^ ^
std::cout << "bounds at positions " << (bounds.first - v.begin());
std::cout << " and " << (bounds.second - v.begin()) << '\n';
// using "mygreater" as comp:
std::sort (v.begin(), v.end(), mygreater); // 30 30 20 20 20 10 10 10
bounds=std::equal_range (v.begin(), v.end(), 20, mygreater); // ^ ^
std::cout << "bounds at positions " << (bounds.first - v.begin());
std::cout << " and " << (bounds.second - v.begin()) << '\n';
return 0;
}
Output：
bounds at positions 3 and 6
bounds at positions 2 and 5
*/
//二分查找法
//注意：[first,last)是已排序
//同样也有两个版本
/*
函数功能：Returns true if any element in the range [first,last) is equivalent to val, and false otherwise.
函数原型：
default (1) ：版本一默认operator<
template
bool binary_search (ForwardIterator first, ForwardIterator last,
const T& val);
custom (2) ：版本二采用仿函数comp
template
bool binary_search (ForwardIterator first, ForwardIterator last,
const T& val, Compare comp);
*/
template
bool binary_search(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_REQUIRES(_Tp, _LessThanComparable);
_ForwardIter __i = lower_bound(__first, __last, __val);//调用二分查找函数，并返回不小于value值的第一个迭代器位置i
return __i != __last && !(__val < *__i);
}
template
bool binary_search(_ForwardIter __first, _ForwardIter __last,
const _Tp& __val,
_Compare __comp) {
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_SAME_TYPE(_Tp,
typename iterator_traits<_ForwardIter>::value_type);
__STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp);
_ForwardIter __i = lower_bound(__first, __last, __val, __comp);//调用二分查找函数，并返回不小于value值的第一个迭代器位置i
return __i != __last && !__comp(__val, *__i);
}
// find_first_of, with and without an explicitly supplied comparison function.
//以[first2,last2)区间内的某些元素为查找目标，寻找他们在[first1,last1)区间首次出现的位置
//find_first_of函数有两个版本：
//版本一：提供默认的equality操作operator==
//版本二：提供用户自行指定的操作规则comp
/*
函数功能：Returns an iterator to the first element in the range [first1,last1) that matches any of the elements in [first2,last2).
If no such element is found, the function returns last1.
函数原型：
equality (1)：版本一
template
ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
predicate (2)：版本二
template
ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
*/
//版本一：提供默认的equality操作operator==
template
_InputIter find_first_of(_InputIter __first1, _InputIter __last1,
_ForwardIter __first2, _ForwardIter __last2)
{
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool,
typename iterator_traits<_InputIter>::value_type,
typename iterator_traits<_ForwardIter>::value_type);
for ( ; __first1 != __last1; ++__first1) //若序列一不为空，则遍历序列一，每次指定一个元素
//以下，根据序列二的每个元素
for (_ForwardIter __iter = __first2; __iter != __last2; ++__iter)
if (*__first1 == *__iter)//若序列一的元素等于序列二的元素，则表示找到
return __first1;//返回找到的位置
return __last1;//否则没找到
}
//版本二：提供用户自行指定的操作规则comp
template
_InputIter find_first_of(_InputIter __first1, _InputIter __last1,
_ForwardIter __first2, _ForwardIter __last2,
_BinaryPredicate __comp)
{
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_REQUIRES(_ForwardIter, _ForwardIterator);
__STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool,
typename iterator_traits<_InputIter>::value_type,
typename iterator_traits<_ForwardIter>::value_type);
for ( ; __first1 != __last1; ++__first1)
for (_ForwardIter __iter = __first2; __iter != __last2; ++__iter)
if (__comp(*__first1, *__iter))
return __first1;
return __last1;
}
//find_first_of函数举例：
/*
#include // std::cout
#include // std::find_first_of
#include // std::vector
#include // std::tolower
bool comp_case_insensitive (char c1, char c2) {
return (std::tolower(c1)==std::tolower(c2));
}
int main () {
int mychars[] = {'a','b','c','A','B','C'};
std::vector haystack (mychars,mychars+6);
std::vector::iterator it;
int needle[] = {'A','B','C'};
// using default comparison:
it = find_first_of (haystack.begin(), haystack.end(), needle, needle+3);
if (it!=haystack.end())
std::cout << "The first match is: " << *it << '\n';
// using predicate comparison:
it = find_first_of (haystack.begin(), haystack.end(),
needle, needle+3, comp_case_insensitive);
if (it!=haystack.end())
std::cout << "The first match is: " << *it << '\n';
return 0;
}
Output:
The first match is: A
The first match is: a
*/
// find_end, with and without an explicitly supplied comparison function.
// Search [first2, last2) as a subsequence in [first1, last1), and return
// the *last* possible match. Note that find_end for bidirectional iterators
// is much faster than for forward iterators.
// find_end for forward iterators.
//若萃取出来的迭代器类型为正向迭代器forward_iterator_tag，则调用此函数
template
_ForwardIter1 __find_end(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2,
forward_iterator_tag, forward_iterator_tag)
{
if (__first2 == __last2)//若第二个区间为空
return __last1;//则直接返回第一个区间的尾端
else {
_ForwardIter1 __result = __last1;
while (1) {
//以下利用search函数查找出某个子序列的首次出现点；若找不到直接返回last1
_ForwardIter1 __new_result
= search(__first1, __last1, __first2, __last2);
if (__new_result == __last1)//若返回的位置为尾端，则表示没找到
return __result;//返回last1
else {//若在[first1,last1)中找到[first2,last2)首次出现的位置，继续准备下一次查找
__result = __new_result;//更新返回的位置
__first1 = __new_result;//更新查找的起始位置
++__first1;//确定正确查找起始位置
}
}
}
}
//版本二：指定规则
template
_ForwardIter1 __find_end(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2,
forward_iterator_tag, forward_iterator_tag,
_BinaryPredicate __comp)
{
if (__first2 == __last2)
return __last1;
else {
_ForwardIter1 __result = __last1;
while (1) {
_ForwardIter1 __new_result
= search(__first1, __last1, __first2, __last2, __comp);
if (__new_result == __last1)
return __result;
else {
__result = __new_result;
__first1 = __new_result;
++__first1;
}
}
}
}
// find_end for bidirectional iterators. Requires partial specialization.
#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
//若萃取出来的迭代器类型为双向迭代器bidirectional_iterator_tag，则调用此函数
template
_BidirectionalIter1
__find_end(_BidirectionalIter1 __first1, _BidirectionalIter1 __last1,
_BidirectionalIter2 __first2, _BidirectionalIter2 __last2,
bidirectional_iterator_tag, bidirectional_iterator_tag)
{
__STL_REQUIRES(_BidirectionalIter1, _BidirectionalIterator);
__STL_REQUIRES(_BidirectionalIter2, _BidirectionalIterator);
//利用反向迭代器很快就可以找到
typedef reverse_iterator<_BidirectionalIter1> _RevIter1;
typedef reverse_iterator<_BidirectionalIter2> _RevIter2;
_RevIter1 __rlast1(__first1);
_RevIter2 __rlast2(__first2);
//查找时将序列一和序列二逆方向
_RevIter1 __rresult = search(_RevIter1(__last1), __rlast1,
_RevIter2(__last2), __rlast2);
if (__rresult == __rlast1)//表示没找到
return __last1;
else {//找到了
_BidirectionalIter1 __result = __rresult.base();//转会正常迭代器
advance(__result, -distance(__first2, __last2));//调整回到子序列的起始位置
return __result;
}
}
//版本二：指定规则comp
template
_BidirectionalIter1
__find_end(_BidirectionalIter1 __first1, _BidirectionalIter1 __last1,
_BidirectionalIter2 __first2, _BidirectionalIter2 __last2,
bidirectional_iterator_tag, bidirectional_iterator_tag,
_BinaryPredicate __comp)
{
__STL_REQUIRES(_BidirectionalIter1, _BidirectionalIterator);
__STL_REQUIRES(_BidirectionalIter2, _BidirectionalIterator);
typedef reverse_iterator<_BidirectionalIter1> _RevIter1;
typedef reverse_iterator<_BidirectionalIter2> _RevIter2;
_RevIter1 __rlast1(__first1);
_RevIter2 __rlast2(__first2);
_RevIter1 __rresult = search(_RevIter1(__last1), __rlast1,
_RevIter2(__last2), __rlast2,
__comp);
if (__rresult == __rlast1)
return __last1;
else {
_BidirectionalIter1 __result = __rresult.base();
advance(__result, -distance(__first2, __last2));
return __result;
}
}
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
// Dispatching functions for find_end.
//find_end函数有两个版本：
//版本一：提供默认的equality操作operator==
//版本二：提供用户自行指定的操作规则comp
//注意：这里也有偏特化的知识
/*函数功能：Searches the range [first1,last1) for the last occurrence of the sequence defined by [first2,last2),
and returns an iterator to its first element, or last1 if no occurrences are found.
函数原型：
equality (1)：版本一
template
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
predicate (2)：版本二
template
ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
*/
//对外接口的版本一
template
inline _ForwardIter1
find_end(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2)
{
__STL_REQUIRES(_ForwardIter1, _ForwardIterator);
__STL_REQUIRES(_ForwardIter2, _ForwardIterator);
__STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool,
typename iterator_traits<_ForwardIter1>::value_type,
typename iterator_traits<_ForwardIter2>::value_type);
//首先通过iterator_traits萃取出first1和first2的迭代器类型
//根据不同的迭代器类型调用不同的函数
return __find_end(__first1, __last1, __first2, __last2,
__ITERATOR_CATEGORY(__first1),
__ITERATOR_CATEGORY(__first2));
}
//对外接口的版本一
template
inline _ForwardIter1
find_end(_ForwardIter1 __first1, _ForwardIter1 __last1,
_ForwardIter2 __first2, _ForwardIter2 __last2,
_BinaryPredicate __comp)
{
__STL_REQUIRES(_ForwardIter1, _ForwardIterator);
__STL_REQUIRES(_ForwardIter2, _ForwardIterator);
__STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool,
typename iterator_traits<_ForwardIter1>::value_type,
typename iterator_traits<_ForwardIter2>::value_type);
//首先通过iterator_traits萃取出first1和first2的迭代器类型
//根据不同的迭代器类型调用不同的函数
return __find_end(__first1, __last1, __first2, __last2,
__ITERATOR_CATEGORY(__first1),
__ITERATOR_CATEGORY(__first2),
__comp);
}
//find_end函数举例：
/*
#include // std::cout
#include // std::find_end
#include // std::vector
bool myfunction (int i, int j) {
return (i==j);
}
int main () {
int myints[] = {1,2,3,4,5,1,2,3,4,5};
std::vector haystack (myints,myints+10);
int needle1[] = {1,2,3};
// using default comparison:
std::vector::iterator it;
it = std::find_end (haystack.begin(), haystack.end(), needle1, needle1+3);
if (it!=haystack.end())
std::cout << "needle1 last found at position " << (it-haystack.begin()) << '\n';
int needle2[] = {4,5,1};
// using predicate comparison:
it = std::find_end (haystack.begin(), haystack.end(), needle2, needle2+3, myfunction);
if (it!=haystack.end())
std::cout << "needle2 last found at position " << (it-haystack.begin()) << '\n';
return 0;
}
Output:
needle1 found at position 5
needle2 found at position 3
*/ 参考资料：
《STL源码剖析》侯捷