Learn point C language (28): Data type

In a structure, the data type of each field is unique; Using unions, you can store different data types in one field.

Different data types share a piece of memory. Of course, its memory size should be based on the big.

The data in the joint, either or, only one is valid; There should be a description of what type is useful at this time in a data.

In addition to shared memory, federation is the same as structure.

1. The size of the union is the size of the largest data member:

#include　<stdio.h>

int　main(void)
{
　　union　MyUnion　{
　　　　short　n1;
　　　　int　　n2;
　　　　double　n3;
　　};

　　printf("%u,　%u\n",　sizeof(union　MyUnion),　sizeof(double));

　　getchar();
　　return　0;
}

2. Union is characterized by shared memory, which modifies one other variable:

#include　<stdio.h>
#include　<limits.h>

int　main(void)
{
　　union　MyUnion　{
　　　　unsigned　char　　　n1;
　　　　unsigned　short　　n2;
　　　　unsigned　int　　　n3;　
　　}　U　=　{0};

　　printf("%10u,　%10u,　%10u\n",　U.n1,　U.n2,　U.n3);

　　U.n2　=　USHRT_MAX;
　　printf("%10u,　%10u,　%10u\n",　U.n1,　U.n2,　U.n3);

　　U.n3　=　INT_MAX;
　　printf("%10u,　%10u,　%10u\n",　U.n1,　U.n2,　U.n3);

　　U.n1　=　0;
　　printf("%10u,　%10u,　%10u\n",　U.n1,　U.n2,　U.n3);

　　getchar();
　　return　0;
}