std :: search_n以及C++中的示例

先决条件：std :: search
std :: search_n是在头文件中定义的STL算法，用于搜索给定元素是否满足谓词(如果未定义谓词，则等于)。容器元素连续的时间。

它在范围[first，last]中搜索一系列计数元素，每个计数元素等于给定值(版本1)或满足谓词(版本2)。

如果找不到这样的序列，则该函数将迭代器返回到此类元素的第一个元素，或者将迭代器返回至容器的最后一个元素。

std :: search_n的两个版本定义如下：

1. 为了使用==比较元素：

   句法：

   ForwardIterator search_n (ForwardIterator first, ForwardIterator last,
                              Size count, const T& val);
   
   first: 
   Forward iterator to beginning of the container to be searched into.
   last: 
   Forward iterator to end of the container to be searched into.
   count: 
   Minimum number of successive elements to match.
   Size shall be (convertible to) an integral type.
   val: Individual value to be compared.
   Returns: 
   It returns an iterator to the first element of the sequence.
   If no such sequence is found, the function returns last.
   

   // C++ program to demonstrate the use of std::search_n
     
   #include 
   #include 
   #include 
   using namespace std;
   int main()
   {
       int i, j;
     
       // Declaring the sequence to be searched into
       vector v1 = { 1, 2, 3, 4, 5, 3, 3, 6, 7 };
     
       // Declaring the value to be searched for
       int v2 = 3;
     
       // Declaring an iterator for storing the returning pointer
       vector::iterator i1;
     
       // Using std::search_n and storing the result in
       // iterator i1
       i1 = std::search_n(v1.begin(), v1.end(), 2, v2);
     
       // checking if iterator i1 contains end pointer of v1 or not
       if (i1 != v1.end()) {
           cout << "v2 is present consecutively 2 times at index "
                << (i1 - v1.begin());
       } else {
           cout << "v2 is not present consecutively 2 times in "
                << "vector v1";
       }
     
       return 0;
   }
   

   输出：

   v2 is present consecutively 2 times at index 5
   

2. 使用谓词比较元素：
   句法：

   ForwardIterator search_n ( ForwardIterator first, ForwardIterator last,
                              Size count, const T& val, BinaryPredicate pred );
   
   All the arguments are same as previous template, just one more argument is added
   
   pred: Binary function that accepts two arguments 
   (one element from the sequence as first, and val as second),
    and returns a value convertible to bool. The value returned indicates whether 
   the element is considered a match in the context of this function.
   The function shall not modify any of its arguments. 
   This can either be a function pointer or a function object.
   
   Returns:
   It also returns value as per the previous version, i.e., 
   an iterator to the first element of the sequence, 
   satisfying a condition with respect to a given value.
   If no such sequence is found, the function returns last.

   // C++ program to demonstrate the use of std::search_n
   // with binary predicate
   #include 
   #include 
   #include 
   using namespace std;
     
   // Defining the BinaryPredicate function
   bool pred(int i, int j)
   {
       if (i == j) {
           return 1;
       } else {
           return 0;
       }
   }
     
   int main()
   {
       int i, j;
     
       // Declaring the sequence to be searched into
       vector v1 = { 1, 2, 3, 4, 5, 3, 3, 6, 7 };
     
       // Declaring the value to be compared to v1 based
       // on a given predicate
       int v2 = 3;
     
       // Declaring an iterator for storing the returning pointer
       vector::iterator i1;
     
       // Using std::search_n and storing the result in
       // iterator i1
       i1 = std::search_n(v1.begin(), v1.end(), 2, v2, pred);
     
       // checking if iterator i1 contains end pointer of v1 or not
       if (i1 != v1.end()) {
           cout << "v2 is present consecutively 2 times at index "
                << (i1 - v1.begin());
       } else {
           cout << "v2 is not present consecutively 2 times "
                << "in vector v1";
       }
     
       return 0;
   }
   

   输出：

   v2 is present consecutively 2 times at index 5
   

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