若要檢視英文版的文章，請選取 [原文] 核取方塊。您也可以將滑鼠指標移到文字上，即可在快顯視窗顯示英文原文。 譯文 原文

# map::operator[]

Visual Studio 2015

## 語法

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

## 參數

 參數 說明 _Key 要插入項目的索引鍵值。

## 備註

operator[] 可用來將項目插入對應 m 使用 DataValuemapped_type 項目的值與 _Key的一個索引鍵值的 m[_Key] = DataValue;

## 範例

```// 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);
}
```
```          對應之項目的索引鍵是:1 2 3。

c2 [移動 (str]== 0
c2 [「abc」] == 1
```