Справочник Пользователя для ABL electronic PIC Microcontrollers PIC18

Union types are derived types sharing many of the syntactic and functional fea-
tures of structure types. The key difference is that a union allows only one of its
members to be “active” at any given time, the most recently changed member.

Note: mikroC does not support anonymous unions (ANSI divergence).

Unions are declared same as structures, with the keyword 

union

used instead of

struct

:

tag { member-declarator-list };

Unlike structures’ members, the value of only one of union’s members can be
stored at any time. Let’s have a simple example:

myunion {  

// union tag is 'myunion'

i;

d;

ch;

} mu, *pm = μ

The identifier 

mu

, of type 

union myunion

, can be used to hold a 2-byte 

int

, a

4-byte 

double

, or a single-byte 

char

, but only one of these at any given time.

The size of a union is the size of its largest member. In our previous example, both

sizeof(union myunion)

and 

sizeof(mu)

return 4, but 2 bytes are unused

(padded) when 

mu

holds an 

int

object, and 3 bytes are unused when 

mu

holds a

char

.

Union members can be accessed with the structure member selectors (

.

and 

->

),

but care is needed. Check the example on the following page.

MikroElektronika:  Development  tools  -  Books  -  Compilers

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page

mikroC - C Compiler for Microchip PIC microcontrollers

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