What is the Meaning of "a : b" in C struct Syntax?

C struct Syntax: Unraveling the Meaning of "a : b"

In C , you may encounter a syntax such as "a : b" when defining members of a struct. Let's explore what this syntax signifies.

Consider the example provided:

struct SMyDataWord
{
    int Name : 40;
    int Colour : 24;
};

The ":" syntax, known as bitfields, is carried over from the C programming language. In this case, it denotes that the members "Name" and "Colour" occupy specific bit ranges within the struct's memory layout.

Specifically, the "Name" member has a width of 40 bits, while the "Colour" member has a width of 24 bits. This means that the first 40 bits of the struct's memory are dedicated to storing the "Name" value, followed by the next 24 bits for the "Colour" value.

By utilizing bitfields, you can conserve memory by packing multiple values into a single data structure, which can be advantageous when dealing with scenarios where space is constrained. However, it's important to note that using bitfields can make your code less portable across different platforms and compilers.

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