Structs

About

Implemented as a derived type (not basic)

What is the difference between Structs and Arrays? Struct’s are heterogenous.

can also be called a record
objects being aggregated are called the fields

Syntax

Anonymous Structure: struct {...} x;

Tagged Structure (T is the tag) struct T {...} x;

You need to use a tagged structure if you want to refer to the same type within the struct itself (e.g., a Linked List node with a field pointing to the next node of the same type)

typedef struct {...} T can be used to define a shorthand synonym for the structure type.

Declaration

The declaration struct T {...} x has the following effect:

Reserves sizeof(struct T) contiguous bytes in memory to hold variable x, starting at some location $M_{x}$ (thus, SIZE(x) = sizeof(struct T))
ADDR(x) $= M_{x}$

Fields of the structure appear in the same order in memory as the declaration

Each field f of the object x has a type of $T_{f}$ and an offset $o \geq 0$ such that the field x.f occupies sizeof( $T_{f}$ ) bytes starting at memory location $M_{x} + o$

The size of the struct is greater than or equal to the sum of the sizes of all it’s fields.

Why greater than?

Accessing

Given struct T{...} x, *xp;

Syntax: x.f or xp->f

R-Value

Returns a value of type TYPE(x.f) by interpreting the bit representation in BOX(x.f)

L-Value

Updates memory bytes of BOX(x.f) with the type-appropriate bit representation of the R-value of the assignment operation. (like setting a variable)

Notes

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