Structure Bitfields in C Programming

Bitfields

• Data items which can be combined to form an individual word of memory are known as bitfields.

Syntax:


struct struct_name
{
    member 1 : size;
    member 2 : size;
    .
    .
    member n : size;
};



• In the above syntax, each member is followed by a semicolon and an unsigned integer which indicates the field size.
• The definition and accessing of every member is the same as the ordinary structure.

Example:
We want to store the details of a student. The information can be:
i) Roll no of a student where 1 bits is sufficient.
ii) Standard or class that it belongs to so 3 bits would be sufficient.

The structure can be declared as follows:


struct student
{
    unsigned roll_no: 1;
    unsigned std : 3;
};



• The above structure is subdivided into 3 bit fields. Their widths are 1 and 3 so they occupy 4 bits within the word of a memory.
• The values to bitfields are assigned using the #define.
• They can also be initialized and even appear in arithmetic expressions.
• Bitfields of arrays are not allowed.
• The '&' operator cannot be added to a bitfield.
• A pointer cannot access a bitfield and a function cannot return a bitfield.
• A bitfield without a name can be used for padding.
• It can be forced for starting of a new beginning by specifying an unnamed bitfield with 0 width.