C Language_(10)_Constructed Data Types_Union(2)

1 Commonwealth (Consortium)

        union

       {

                Data type 1 member variable 1;

                Data type 2 member variable 2;

                data type 3 member variable 3;

        }；

                Union All member variables share the same space.

                And if you change any member value later, the previous value will not count.

For example, the following example

#include <stdio.h>

union data
{
	char a;
	short b;
	int c;
};

int main(int argc, const char *argv[])
{
	union data data1;
	data1.a = 'A';
	printf("data1.a = %c\n",data1.a);

	data1.b = 100;
	printf("data1.b = %d\n",data1.b);

	data1.c = 1100;
	printf("data1.c = %d\n",data1.c);

	
	return 0;
}

operation result

 

2 Memory size endianness

1 Memory little endian: memory low address stores low data bits, memory high address stores high data bits (computers are generally little endian)

2 Memory big end: memory low address stores high data bit, memory high address stores low data bit (hardware such as ARM storage is big endian)

***How ​​to judge whether your device is endian? ***

#include <stdio.h>
union big_small_d
{
          int bsd1;
          char bsd2;
};

int main(int argc, char const *argv[])
{
     union big_small_d data;

     data.bsd1 = 1;
          if (data.bsd2)
          {
                    printf("为小端\n");
          }
          else 
          {
                    printf("为大端\n");
          }

          return 0;
}