C Language Basics Tutorial (iv) Pointers, structures, unions, and enumerations (15)

Union (Union)

1. Joint notes and joint variable definitions
Union is also a new type of data, which is a special form of variable.
The joint description and the union variable definitions are very similar to the structure. In the form of:
Union Union name {
Data type member name;
Data type member name;
...
Union variable name;
A union represents several variables common to one memory location, which holds different data types and variables of varying lengths at different times.
The following example shows a joint A_BC:
Union a_bc{
int i;
char mm;
};
You can then define union variables with the indicated union.
For example, a union variable named LGC is defined with the union described above, which can be written as:
Union A_BC LGC;
In union variable LGC, integer i and character mm share the same memory location.
When a union is described, the compiler automatically produces a variable of the length of the largest variable in the union.
The method of joint access to its members is the same as the structure. The same union variable can also define an array or pointer, but when defined as a pointer, it also uses the "->" symbol, at which point the federated access member can be represented as:
Union name-> member name
In addition, a union can appear within a structure, and its members can also be structs.
For example:
struct{
int age;
Char *addr;
union{
int i;
Char *ch;
}x;
}Y[10];
To access member I of Union x in struct variable y[1], you can write:
Y[1].X.I;
To access the string pointer to union x in struct variable y[2] The first character of CH characters is written as:
*y[2].x.ch;
If written "Y[2].X.*CH;" Is wrong.