how to declare an unsigned int in a C program

Question

On this link I came across http://lxr.linux.no/#linux+v2.6.36/include/linux/pci.h#L299 integer declaration unsigned int is_added:1;I have made C programs and declared integers in them but in the above I see use of : What sort of syntax is that?

Answer 1

I think you have come across a bit-field :)

Answer 2

It's part of a struct, which means that it indicates that the field should only use a certain number of bits instead of an entire byte or more.

Answer 3

This is bit field declaration in an array. The number post ":" denotes number of bits to allocate to this particular field of the structure.

Although you need to be careful with bit-fields as their binary representation is not portable. That is you are passing binary blobs between interfaces compiled with different compilers it may not work.

Answer 4

This indicates that only one bit of this will be used.

Answer 5

In structs, one can have integer variables that occupy any number of bits between 1 and 31. is_added is such a one-bit variable. One-bit variables are also known as flags.