Union union

The union is a data format capable of storing various types of data, but only while the memory wherein one type.

. 1  Union one4all
 2  {
 . 3      int int_val;
 . 4      Double double_val;
 . 5      Long long_val;
 . 6  };
 . 7  
. 8  one4all Pail;
 . 9 pail.int_val = . 4 ; // Pail storage type int. 4 
10 pail.double_val = 4.9 ; // Pail this when storing double type 4.9, 4 before it was abandoned

Each union can store a value, it must have enough space to store the largest member, so that the common length of the body length is typically the largest member.

Use: When two or more items of data formats (but will not be used at the same time), save space.

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Anonymous union anonymous union

 1 union widget
 2 {
 3     char brand[10];
 4     int type;
 5     union
 6     {
 7         long id_num;
 8         char id_char[20];
 9     };
10 };
11 
12 widget prize;
13 if (prize.type == 1) 
14     cin >> prize.id_num;
15 else
16     cin >>prize.id_char;