Equal()函数的用法

函数语法：

1、template bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 ); 2、template bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, BinaryPredicate pred );

函数用法：

测试是否在两个范围的元素都是平等的

Compares the elements in the range [first1,last1) with those in the range beginning at first2, and returns true if the elements in both ranges are considered equal.

The elements are compared by either applying the == comparison operator to each pair of corresponding elements, or the template parameter comp (for the second version).

这个函数模板的行为等于：

template <class InputIterator1, class InputIterator2>
  bool equal ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2 )
{
  while ( first1!=last1 )
  {
    if (*first1 != *first2)   // or: if (!pred(*first1,*first2)), for pred version
      return false;
    ++first1; ++first2;
  }
  return true;
}

参数注释：

   first1, last1：

      Forward iterators to the initial and final positions of the first sequence. The range used is [first1,last1), which contains all the elements between first1 and last1, including the element pointed by first1 but not the element pointed by last1.           

first2：

Forward iterator to the initial position of the second sequence. The comparison includes up to as many elements in this sequence as in the above sequence.。

pred：

Binary predicate taking two elements as argument (one of each of the two sequences), and returning the result of the comparison between them, with true (non-zero) meaning that they are to be considered equal, and false (zero) that they are not-equal. This can either be a pointer to a function or an object whose class overloads operator().

返回值：

#include
#include
#include
using namespace std;
class student{
    public:
        int No,grade;
        student(int No,int grade):No(No),grade(grade){};
        bool operator==(student& s){
            return this->grade==s.grade;
        }
};
int main(){
    vectorv1;
    student s1(1000,100);
    student s2(1001,98);
    student s3(1002,96);
    student s4(1003,94);
    v1.push_back(s1);
    v1.push_back(s2);
    v1.push_back(s3);
    v1.push_back(s4);
    vectorv2;
    v2=v1;
    if(equal(v1.begin(),v1.end(),v2.begin())){
        cout<<"yes"<
    }
}

true if all the elements in the range [first1,last1) compare equal to those of the range starting at first2, and false otherwise.

 #include
 #include
 #include
 using namespace std;
 class student{
     public:
         int No,grade;
         student(int No,int grade):No(No),grade(grade){};
     /*  bool operator==(student& s){
             return this->grade==s.grade;
         }*/
 };
 bool cmp(student& s1,student& s2){
     return s1.grade==s2.grade;
 }
 int main(){
     vectorv1;
     student s1(1000,100);
     student s2(1001,98);
     student s3(1002,96);
     student s4(1003,94);
     v1.push_back(s1);
     v1.push_back(s2);
     v1.push_back(s3);
     v1.push_back(s4);
     vectorv2;
     v2=v1;
     if(equal(v1.begin(),v1.end(),v2.begin(),cmp)){
         cout<<"yes"<
     }
 }