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. | + | In the example below - Alarmclock data structure - 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> | ||
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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 ( 0 to 9 ) |
| − | unsigned digit2 : 4; // Hour LSD 7 segment | + | unsigned digit2 : 4; // Hour LSD 7 segment ( 0 to 9 ) |
| − | unsigned digit3 : 4; // Minute MSD 7 segment | + | unsigned digit3 : 4; // Minute MSD 7 segment ( 0 to 9 ) |
| − | unsigned digit4 : | + | unsigned digit4 : 2; // minute LSD 7 segment ( 0 to 2 ) |
| − | unsigned | + | unsigned alarm1 : 4; // Alarm Hour MSD 7 segment ( 0 to 9 ) |
| − | unsigned | + | unsigned alarm2 : 4; // Alarm Hour LSD 7 segment ( 0 to 9 ) |
| + | unsigned alarm3 : 4; // Alarm Minute MSD 7 segment ( 0 to 9 ) | ||
| + | unsigned alarm4 : 2; // Alarm minute LSD 7 segment ( 0 to 2 ) | ||
}; | }; | ||
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} | } | ||
</source> | </source> | ||
| + | |||
=Links= | =Links= | ||
*[http://publib.boulder.ibm.com/infocenter/macxhelp/v6v81/index.jsp?topic=%2Fcom.ibm.vacpp6m.doc%2Flanguage%2Fref%2Fclrc03defbitf.htm IBM on C bitfields] | *[http://publib.boulder.ibm.com/infocenter/macxhelp/v6v81/index.jsp?topic=%2Fcom.ibm.vacpp6m.doc%2Flanguage%2Fref%2Fclrc03defbitf.htm IBM on C bitfields] | ||
Revision as of 09:34, 26 August 2012
C and C++ programming
In the example below - Alarmclock data structure - 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 ( 0 to 9 )
unsigned digit2 : 4; // Hour LSD 7 segment ( 0 to 9 )
unsigned digit3 : 4; // Minute MSD 7 segment ( 0 to 9 )
unsigned digit4 : 2; // minute LSD 7 segment ( 0 to 2 )
unsigned alarm1 : 4; // Alarm Hour MSD 7 segment ( 0 to 9 )
unsigned alarm2 : 4; // Alarm Hour LSD 7 segment ( 0 to 9 )
unsigned alarm3 : 4; // Alarm Minute MSD 7 segment ( 0 to 9 )
unsigned alarm4 : 2; // Alarm minute LSD 7 segment ( 0 to 2 )
};
void main(void) {
struct display d;
printf("Structure size: %i\n", (int) sizeof d);
}
Links
- IBM on C bitfields
- Using Bitfields Effectively (volatile example)