Difference between revisions of "Bitfields programming"
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=C and C++ programming= | =C and C++ programming= | ||
| − | + | In the example below the complete structure will live in 4 bytes on a 32 bit memorysystem. | |
<source lang=c> | <source lang=c> | ||
#include <stdio.h> | #include <stdio.h> | ||
| − | |||
struct display { | struct display { | ||
unsigned format : 1; // 24 hour or 12 hour format | unsigned format : 1; // 24 hour or 12 hour format | ||
unsigned pm : 1; // PM and AM leds. If 12 hour format pm or am (pm=0 is am) | unsigned pm : 1; // PM and AM leds. If 12 hour format pm or am (pm=0 is am) | ||
| − | unsigned alarm : 1; // Alarm on/off LED. | + | unsigned alarm : 1; // Alarm on/off LED. |
unsigned digit1 : 4; // Hour MSD 7 segment | unsigned digit1 : 4; // Hour MSD 7 segment | ||
unsigned digit2 : 4; // Hour LSD 7 segment | unsigned digit2 : 4; // Hour LSD 7 segment | ||
unsigned digit3 : 4; // Minute MSD 7 segment | unsigned digit3 : 4; // Minute MSD 7 segment | ||
| − | unsigned | + | unsigned digit4 : 4; // minute LSD 7 segment |
| + | unsigned date : 5; // Date 1. to 31. | ||
| + | unsigned month : 4; // Month 1 to 12 | ||
}; | }; | ||
| + | |||
| + | void main(void) { | ||
| + | struct display d; | ||
| + | printf("Structure size: %i\n", (int) sizeof d); | ||
| + | } | ||
</source> | </source> | ||
=Links= | =Links= | ||
Revision as of 09:11, 26 August 2012
C and C++ programming
In the example below the complete structure will live in 4 bytes on a 32 bit memorysystem.
#include <stdio.h>
struct display {
unsigned format : 1; // 24 hour or 12 hour format
unsigned pm : 1; // PM and AM leds. If 12 hour format pm or am (pm=0 is am)
unsigned alarm : 1; // Alarm on/off LED.
unsigned digit1 : 4; // Hour MSD 7 segment
unsigned digit2 : 4; // Hour LSD 7 segment
unsigned digit3 : 4; // Minute MSD 7 segment
unsigned digit4 : 4; // minute LSD 7 segment
unsigned date : 5; // Date 1. to 31.
unsigned month : 4; // Month 1 to 12
};
void main(void) {
struct display d;
printf("Structure size: %i\n", (int) sizeof d);
}
Links
- IBM on C bitfields
- Using Bitfields Effectively (volatile example)