map::operator

将元素插入到具有指定的键值的映射中。

Type& operator[](
   const Key& _Key
);
Type& operator0-(
    Key&& _Key
);

参数

返回值

对于插入的元素数据值的引用。

备注

如果找不到参数的键值，则它与数据类型以及的默认插入。

operator[] 能用于将元素插入到映射 m 使用 DataValue 是元素 mapped_type 的值与 _Key的键值的 m[_Key] = DataValue;。

在使用 operator[] 插入元素时，返回的引用不指示插入是否更改预先存在的组件或创建新的。成员函数 查找 和 插入 可用于确定与指定的键的元素是否在插入之前已存在。

示例

// map_op_insert.cpp
// compile with: /EHsc
#include <map>
#include <iostream>
#include <string>

int main( )
{
   using namespace std;
   typedef pair <const int, int> cInt2Int;
   map <int, int> m1;
   map <int, int> :: iterator pIter;
   
   // Insert a data value of 10 with a key of 1
   // into a map using the operator[] member function
   m1[ 1 ] = 10;

   // Compare other ways to insert objects into a map
   m1.insert ( map <int, int> :: value_type ( 2, 20 ) );
   m1.insert ( cInt2Int ( 3, 30 ) );

   cout  << "The keys of the mapped elements are:";
   for ( pIter = m1.begin( ) ; pIter != m1.end( ) ; pIter++ )
      cout << " " << pIter -> first;
   cout << "." << endl;

   cout  << "The values of the mapped elements are:";
   for ( pIter = m1.begin( ) ; pIter != m1.end( ) ; pIter++ )
      cout << " " << pIter -> second;
   cout << "." << endl;

   // If the key already exists, operator[]
   // changes the value of the datum in the element
   m1[ 2 ] = 40;

   // operator[] will also insert the value of the data
   // type's default constructor if the value is unspecified
   m1[5];

   cout  << "The keys of the mapped elements are now:";
   for ( pIter = m1.begin( ) ; pIter != m1.end( ) ; pIter++ )
      cout << " " << pIter -> first;
   cout << "." << endl;

   cout  << "The values of the mapped elements are now:";
   for ( pIter = m1.begin( ) ; pIter != m1.end( ) ; pIter++ )
      cout << " " << pIter -> second;
   cout << "." << endl;

// insert by moving key
    map<string, int> c2;
    string str("abc");
    cout << "c2[move(str)] == " << c2[move(str)] << endl;
    cout << "c2["abc"] == " << c2["abc"] << endl;

    return (0); 
}

要求

标头: <map>

命名空间: std

请参见

参考

map Class

标准模板库