C++ Union structure
Angie An
  2023-12-15 11:21:29 2023-12-15 11:21  

C++ The union Data Structure

A union is like a struct in that it generally has several fields, all of which are public by default. Unlike a struct, however, only one of the fields is used at any given time.

In other words, it is a structure that allows the same storage space to be used to store values of different data types at different times.

Unions can be used to conserve memory when a structure is needed in which several pieces of information of different types must be represented but only one will be used at a time, as when the components of a container must contain values of differing data types.

The usual syntax for a union is illustrated by

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union Test{
	struct{
		int x;
		int y;
		int z;
	}s;
		int k;
}myUnion;
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int main()
{
	myUnion.s.x = 4;
	myUnion.s.y = 5;
	myUnion.s.z = 6;
	myUnion.k = 0;
	cout<< myUnion.s.x <<endl;
	cout<< myUnion.s.y <<endl;
	cout<< myUnion.s.z <<endl;
	cout<< myUnion.k <<endl;
}

When the above code is executed, the program will output the following result

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0
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0

对k的赋值因为是union，要共享内存，所以从union的首地址开始放置，首地址开始的位置其实是x的位置，这样原来内存中x的位置就被k所赋的值代替了，就变为0了。

And this is basically how union works.

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