Basic doubt in C structure

cbalu · 08-14-2009, 12:58 AM

Hi all,

I was navigating inside linux kernel code and inside that one i have seen few structures which are very strange (for me). The structure is of the following form

Code:

struct dummy {
     int a:1;
     unsigned long b:5;
};

In the above structure does anyone explain me what is the number after the : will do.

Thanks in advance
-BalaC-

Sebastiani · 08-14-2009, 01:08 AM

It's called a bitfield.

Brafil · 08-17-2009, 11:03 AM

a is a bitfield (like an int or char, but with one bit). b too, but with five bits. "a = 2" will probably give 0, since the upper bits are chopped off.

08-14-2009, 12:58 AM	#1
cbalu Registered User Join Date: May 2009 Location: Chennai, India Posts: 17	Basic doubt in C structure Hi all, I was navigating inside linux kernel code and inside that one i have seen few structures which are very strange (for me). The structure is of the following form Code: struct dummy { int a:1; unsigned long b:5; }; In the above structure does anyone explain me what is the number after the : will do. Thanks in advance -BalaC-
cbalu is offline

08-14-2009, 01:08 AM	#2
Sebastiani Guest Join Date: Aug 2001 Posts: 4,923	It's called a bitfield.
Sebastiani is offline

08-17-2009, 11:03 AM	#3
Brafil Making mistakes Join Date: Dec 2008 Posts: 347	a is a bitfield (like an int or char, but with one bit). b too, but with five bits. "a = 2" will probably give 0, since the upper bits are chopped off. __________________ Look at this: Community Project And this: Ascent - Programmer needed
Brafil is offline

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