代码如下

#include <iostream>
#include <string>
using namespace std;

typedef struct t_in_struct1
{
	int var1;
	int var2;
}name_in_struct1;

typedef struct t_in_struct2
{
	int var3;
	int var4;
}name_in_struct2;

typedef struct t_struct {
	int a;
	union {
		name_in_struct1 in_struct1;
		name_in_struct2 in_struct2;
	}union_name;
}name_struct;

int main() {
	name_struct structA;
	structA.a = 0;
	structA.union_name.in_struct1.var1 = 1;
	structA.union_name.in_struct1.var2 = 2;
	structA.union_name.in_struct2.var3 = 3;
	structA.union_name.in_struct2.var4 = 4;

	cout << "0 "<<endl;

	cout << "structA.a = " << structA.a << endl;
	cout << "structA.union_name.in_struct1.var1 = " << structA.union_name.in_struct1.var1 << endl;
	cout << "structA.union_name.in_struct1.var2 = " << structA.union_name.in_struct1.var2 << endl;
	cout << "structA.union_name.in_struct2.var3 = " << structA.union_name.in_struct2.var3 << endl;
	cout << "structA.union_name.in_struct2.var4 = " << structA.union_name.in_struct2.var4 << endl;

	cout << "1 " << endl;
	return 0;
}

结果如下