equal和mismatch算法的功能是比较容器中的两个区间内的元素。这两个算法各有3个参数first1,last1和first2.如果对 于区间[first1,last1)内所有的first1+i,first1+i和first2所在位置处的元素都相等,则equal算法返回真,否则返 回假。mismatch算法的返回值是由两个迭代器first1+i和first2+i组成的一个pair,表示第1对不相等的元素的位置。如果没有找到 不相等的元素,则返回last1和first2+(last1-first1)。因此,语句equal(first1,last1,first2)和mismatch(first1,last1,first2).first==last1是等价的.
1 // Illustrating the generic equal and mismatch algorithms
2 #include <iostream>
3 #include <cassert>
4 #include <algorithm>
5 #include <string>
6 #include <list>
7 #include <deque>
8 #include <vector>
9 using namespace std;
10
11 int main()
12 {
13 cout << "Illustrating the generic equal "
14 << "and mismatch algorithms." << endl;
15 list<string> driver_list;
16 vector<string> vec;
17 deque<string> deq;
18
19 driver_list.insert(driver_list.end(), "Clark");
20 driver_list.insert(driver_list.end(), "Rindt");
21 driver_list.insert(driver_list.end(), "Senna");
22
23 vec.insert(vec.end(), "Clark");
24 vec.insert(vec.end(), "Rindt");
25 vec.insert(vec.end(), "Senna");
26 vec.insert(vec.end(), "Berger");
27
28 deq.insert(deq.end(), "Clark");
29 deq.insert(deq.end(), "Berger");
30
31 // Show that driver_list and the first 3 elements of
32 // vec are equal in all corresponding positions:
33 assert (equal(driver_list.begin(), driver_list.end(),
34 vec.begin()));
35
36 // Show that deq and the first 2 elements of driver_list
37 // are not equal in all corresponding positions:
38 assert (!equal(deq.begin(), deq.end(),
39 driver_list.begin()));
40
41 // Find the corresponding positions in deq and driver_list
42 // at which unequal elements first occur:
43 pair<deque<string>::iterator, list<string>::iterator>
44 pair1 = mismatch(deq.begin(), deq.end(),
45 driver_list.begin());
46
47 if (pair1.first != deq.end())
48 cout << "First disagreement in deq and driver_list:\n "
49 << *(pair1.first) << " and " << *(pair1.second)
50 << endl;
51 return 0;
52 }
equal算法类似于mismatch,equal算法也是逐一比较两个序列的元素是否相等,只是equal函数的返回值为bool值 true/false,不是返回迭代器值。它有如下两个原型,如果迭代器区间[first1,last1)和迭代器区间[first2, first2+(last1 - first1))上的元素相等(或者满足二元谓词判断条件binary_pred) ,返回true,否则返回false。
函数原型:
1 template<class InputIterator1, class InputIterator2>
2 bool equal(
3 InputIterator1 _First1,
4 InputIterator1 _Last1,
5 InputIterator2 _First2
6 );
7 template<class InputIterator1, class InputIterator2, class BinaryPredicate>
8 bool equal(
9 InputIterator1 _First1,
10 InputIterator1 _Last1,
11 InputIterator2 _First2,
12 BinaryPredicate _Comp
13 );
14
example:
利用二元谓词判断条件absEqual,判断出两个vector向量容器的元素均绝对值相等。
1 #include <algorithm>
2 #include <vector>
3 #include <iostream>
4
5 using namespace std;
6
7 bool absEqual(int a, int b)
8 {
9 return (a == abs(b) || b == abs(a)) ? true : false;
10 }
11
12 int main()
13 {
14 vector<int> ivect1(5);
15 vector<int> ivect2(5);
16
17 for (vector<int>::size_type i = 0; i < ivect1.size(); ++i)
18 {
19 ivect1[i] = i;
20 ivect2[i] = (-1) * i;
21 }
22 if ( equal( ivect1.begin(), ivect1.end(), ivect2.begin(), absEqual ) )
23 {
24 cout << "ivect1 和 ivect2 元素的绝对值完全相等" << endl;
25 }
26 else
27 {
28 cout << "ivect1 和 ivect2 元素的绝对值不完全相等" << endl;
29 }
30 return 0;
31 }