6.7.1 单纯的数据处理
1、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
*/
2、count和count_if
//count：计算指定元素的个数
//count_if：计算满足仿函数pred的条件的元素的个数
//SGI STL中提供两个版本，但是C++标准只提供一种版本
/*功能：Returns the number of elements in the range [first,last) that compare equal to val.
C++标准只提供一种count原型：
template
typename iterator_traits::difference_type
count (InputIterator first, InputIterator last, const T& val);
*/
//SGI STL提供的版本一count，不是C++标准，计数n由参数提供：默认使用operator==
template
void count(_InputIter __first, _InputIter __last, const _Tp& __value,
_Size& __n) {
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_REQUIRES(typename iterator_traits<_InputIter>::value_type,
_EqualityComparable);
__STL_REQUIRES(_Tp, _EqualityComparable);
//将区间[first,last)内的元素和指定值value比较
//若没到达区间尾端，继续查找
for ( ; __first != __last; ++__first)
if (*__first == __value)//若存在相等的值
++__n;//计数器累加1
}
/*功能：Returns the number of elements in the range [first,last) for which pred is true.
C++标准只提供一种count_if原型：
template
typename iterator_traits::difference_type
count_if (InputIterator first, InputIterator last, UnaryPredicate pred);
*/
//SGI STL提供的版本一count_if，不是C++标准：默认使用operator==
template
void count_if(_InputIter __first, _InputIter __last, _Predicate __pred,
_Size& __n) {
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_UNARY_FUNCTION_CHECK(_Predicate, bool,
typename iterator_traits<_InputIter>::value_type);
//将区间[first,last)内的元素和指定值value比较
//若没到达区间尾端，继续查找
for ( ; __first != __last; ++__first)
if (__pred(*__first))//存在符合规则的元素
++__n;//计数器累加1
}
#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
//SGI STL提供的版本二count，也C++标准提供的版本
template
typename iterator_traits<_InputIter>::difference_type
count(_InputIter __first, _InputIter __last, const _Tp& __value) {
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_REQUIRES(typename iterator_traits<_InputIter>::value_type,
_EqualityComparable);
__STL_REQUIRES(_Tp, _EqualityComparable);
typename iterator_traits<_InputIter>::difference_type __n = 0;
//将区间[first,last)内的元素和指定值value比较
//若没到达区间尾端，继续查找
for ( ; __first != __last; ++__first)
if (*__first == __value)//存在相等的元素
++__n;//计数器累加1
return __n;
}
//SGI STL提供的版本二count_if，也C++标准提供的版本
template
typename iterator_traits<_InputIter>::difference_type
count_if(_InputIter __first, _InputIter __last, _Predicate __pred) {
__STL_REQUIRES(_InputIter, _InputIterator);
__STL_UNARY_FUNCTION_CHECK(_Predicate, bool,
typename iterator_traits<_InputIter>::value_type);
typename iterator_traits<_InputIter>::difference_type __n = 0;
//将区间[first,last)内的元素和指定值value比较
//若没到达区间尾端，继续查找
for ( ; __first != __last; ++__first)
if (__pred(*__first))//存在符合规则的元素
++__n;//计数器累加1
return __n;
}
//下面针对count和count_if函数举例：
/*
#include // std::cout
#include // std::count
#include // std::vector
bool IsOdd (int i) { return ((i%2)==1); }
int main () {
// counting elements in array:
int myints[] = {10,20,31,30,21,10,11,20}; // 8 elements
int mycount = std::count (myints, myints+8, 10);
std::cout << "10 appears " << mycount << " times.\n";
// counting elements in container:
std::vector myvector (myints, myints+8);
mycount = std::count (myvector.begin(), myvector.end(), 20);
std::cout << "20 appears " << mycount << " times.\n";
mycount = count_if (myvector.begin(), myvector.end(), IsOdd);
std::cout << "myvector contains " << mycount << " odd values.\n";
return 0;
}
Output:
10 appears 2 times.
20 appears 2 times.
myvector contains 3 odd values.
*/
3、 find 和 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
*/
4、find_end
//在序列[first1,last1)中查找序列[first2,last2)最后一次出现的位置
// 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
*/
5、 find_first_of
// 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
