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How to Declare a Pointer to a Struct in C?

Structure (or structs) in the C programming language provides a way to combine variables of several data types under one name and pointers provide a means of storing memory addresses. In this article, we will learn how to declare such a pointer to a struct in C.

Declaration of Pointer to Struct in C

To declare a pointer to a struct we can use the struct keyword. First, define a structure then declare a pointer to that structure using the below syntax and that pointer can be used to allocate and access memory for the structure.

Syntax of Declaring Pointer to Struct

C program to declare pointer to struct.

The below example demonstrates declaration of pointer to a structure.

To know more, refer to the article - Structure Pointer in C

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15.13 Structure Assignment

Assignment operating on a structure type copies the structure. The left and right operands must have the same type. Here is an example:

Notionally, assignment on a structure type works by copying each of the fields. Thus, if any of the fields has the const qualifier, that structure type does not allow assignment:

See Assignment Expressions .

When a structure type has a field which is an array, as here,

structure assigment such as r1 = r2 copies array fields’ contents just as it copies all the other fields.

This is the only way in C that you can operate on the whole contents of a array with one operation: when the array is contained in a struct . You can’t copy the contents of the data field as an array, because

would convert the array objects (as always) to pointers to the zeroth elements of the arrays (of type struct record * ), and the assignment would be invalid because the left operand is not an lvalue.

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Pointers to Structures in C

If you have defined a derived data type using the keyword struct , then you can declare a variable of this type. Hence, you can also declare a pointer variable to store its address. A pointer to struct is thus a variable that refers to a struct variable.

Syntax: Defining and Declaring a Structure

This is how you will define a new derived data type using the " struct " keyword −

You can then declare a variable of this derived data type as following −

You can then declare a pointer variable and store the address of var . To declare a variable as a pointer, it must be prefixed by " * "; and to obtain the address of a variable, we use the " & " operator.

Accessing the Elements of a Structure

To access the elements of a structure with pointer , we use a special operator called the indirection operator (→) .

Here, we define a user-defined struct type called book . We declare a book variable and a pointer.

To store the address, use the & operator.

Using the Indirection Operator

In C programming, we use the indirection operator (" → ") with struct pointers. It is also called the "struct dereference operator". It helps to access the elements of a struct variable to which the pointer references to.

To access an individual element in a struct, the indirection operator is used as follows −

The struct pointer uses the indirection operator or the dereference operator to fetch the values of the struct elements of a struct variable. The dot operator (" . ") is used to fetch the values with reference to the struct variable. Hence,

Example: Pointers to Structures

The following program shows the usage of pointers to structures. In this example, "strptr" is a pointer to the variable "struct book b1". Hence, "strrptr → title" returns the title, similar to "b1.title" does.

Points to Note

The dot operator (.) is used to access the struct elements via the struct variable.
To access the elements via its pointer, we must use the indirection operator (→).

Let's consider another example to understand how pointers to structures actually work. Here, we will use the keyword struct to define a new derived data type called person and then we will declare a variable of its type and a pointer.

The user is asked to input the name, age and weight of the person. The values are stored in the structure elements by accessing them with the indirection operator.

When you runt this program, it will produce the following output −

C allows you to declare an "array of struct" as well as an "array of pointers". Here, each element in the struct pointer array is a reference to a struct variable.

A struct variable is like a normal variable of primary type, in the sense that you can have an array of struct, you can pass the struct variable to a function, as well as return a struct from a function.

Note : You need to prefix " struct type " to the name of the variable or pointer at the time of declaration. However, you can avoid it by creating a shorthand notation using the typedef keyword.

Why Do We Need Pointers to Structures?

Pointers to structures are very important because you can use them to create complex and dynamic data structures such as linked lists, trees, graphs, etc. Such data structures use self-referential structs , where we define a struct type having one of its elements as a pointer to the same type.

An example of a self-referential structure with a pointer to an element of its own type is defined as follows −

We shall learn about self-referential structures in the next chapter.