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what does int data:4 means

 
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guest
Guest
what does int data:4 means
PostPosted: Wed Jun 30, 2004 6:27 am     Reply with quote
int data define a integer, what 4 means, does 4 is the default value?
dyeatman



Joined: 06 Sep 2003
Posts: 1912
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data:4
PostPosted: Wed Jun 30, 2004 7:10 am     Reply with quote
No, a default value is assigned with int data=4;

It is a bit width definition normally used in a struct.

For more information see page 64 of the CCS C manual where it is shown.
Ttelmah
Guest
Re: what does int data:4 means
PostPosted: Wed Jun 30, 2004 10:12 am     Reply with quote
guest wrote:
int data define a integer, what 4 means, does 4 is the default value?

This is the standard C declaration for a '4bit' value. You can store sizes smaller than an integer 'inside' an integer, using the ':' to specify the number of bits required. This can be very useful to access multiple 'parts' of a register for instance, so if you declare a structure, with:
struct fred {
int8 address:4;
int8 goflag:1;
int8 error:2;
int8 marker:1;
} register;

and then 'locate' it to a particular memory spot, you can access the first four bits of the byte at that point, using:
register.address

and the next bit in the same byte as:
register.goflag

This is a very useful way of talking to 'parts' of a byte.
On it's own, the declaration means that 'data' is now a 4bit number, able to hold 0..15 only.

Best Wishes
Guest
PostPosted: Wed Jun 30, 2004 10:58 am     Reply with quote
Thank you both of you:

I raised this question because I found a definition like this in lcd.c

struct lcd_pin_map {
Boolean enable;
Boolean ers;
Boolean ws;
Boolean unused;
int data: 4;
} lcd;


struct lcd_pin_map const LCD_READ={0,0,0,0,15};
set_tris_lcd(LCD_READ); //set_tris_lcd(LCD_READ) equals set_tris_b(LCD_READ)

and set_tris_b(value); hocome the struct become value define in set_tris_b(value)

so right now the LCD_READ=00001111, right?
Ttelmah
Guest
PostPosted: Wed Jun 30, 2004 2:26 pm     Reply with quote
Yes. :-)
Jeprox
Guest
PostPosted: Wed Jun 30, 2004 4:34 pm     Reply with quote
In C, check out the topic on Bit Field.
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