In the C programming language, a nested structure is a data structure that contains another data structure within it. This means that a structure can be a member of another structure, creating a hierarchy of related data.
Before understanding nested structure we have to understand what is structure in c.
What is Structure in C Programming Language?
In C, The structure is a user-defined data type that is used to store a group of items of different data types as a single data type. Each element of a structure is known as its member.
Syntax of Structure in C
The syntax of structure in C language:
struct struct_Name
{
// Members of the structure
int studentId;
float marks;
};Suppose we have an entity ‘Student’, and we need the name and student id of each student. Instead of storing all the names and ids of each student in some array or vector, we can create a structure ‘Student’ in the following manner:
Example of Structure in C
A simple example of structure in C language is discussed below:
struct Student
{
char name[30];
int studentId;
};Now, We have a brief understanding of Structure in C.
What is Nested Structure in C?
In C, a structure is defined using the struct keyword, followed by the structure name, and then the structure members enclosed within curly braces.
Syntax of Nested Structure in C
Below is the syntax of nested structure in C language:
struct outer_struct {
// outer structure members
int outer_member1;
float outer_member2;
// nested structure definition
struct inner_struct {
// inner structure members
int inner_member1;
float inner_member2;
} inner;
};Example of Nested Structure in C
struct school{
int numberOfStudents;
int numberOfTeachers;
struct student{
char name[50];
int class;
int roll_Number;
} std;
};Explanation:
In the above example of nested structure in C, there are two structures Student (depended structure) and another structure called School(Outer structure). The structure School has the data members like numberOfStudents, numberOfTeachers, etc. and the Student structure is nested inside the structure School and it has the data members like name, class, roll_Number, etc.
To access the members of the school structure, you use dot notation. For example, to access the numberOfStudents member of the school structure, you would use the following syntax:
struct school s;
s.numberOfStudents = 100;To access the members of the nested student structure, you would use the following syntax:
strcpy(s.std.name, "John Smith");
s.std.class = 10;
s.std.roll_Number = 1;Note that the dot notation is used to access the members of the std structure, which is a member of the school structure.
The nested structure student contains three members: name, class, and roll_Number. This structure can be useful in situations where you need to store information about a student, such as their name, class, and roll number.
Ways in Which a Structure Can Be Nested
The structure can be nested in the following different ways:
- By Separate Nested Structure
- By Embedded Nested Structure.
-
By Separate Nested Structure: In this method, the two structures are created, but the dependent structure(Employee) should be used inside the main structure(Organisation) as a member. For a better understanding let’s see an example of separate nested structure in c language.
C Program implemented by Separate Nested Structure
#include <stdio.h> struct employee{ char name[50]; int id; int age; }; struct organisation{ char name[50]; int id; struct employee emp; }; int main(){ struct organisation org1 = {"XYZ Ltd.", 123, {"John Doe", 101, 30}}; printf("Organisation name: %s\n", org1.name); printf("Organisation ID: %d\n", org1.id); printf("Employee name: %s\n", org1.emp.name); printf("Employee ID: %d\n", org1.emp.id); printf("Employee age: %d\n", org1.emp.age); return 0; }Output
Organisation name: XYZ Ltd. Organisation ID: 123 Employee name: John Doe Employee ID: 101 Employee age: 30In this approach, the employee structure is declared separately from the organisation structure. Then, a member of the employee structure is included in the organisation structure as struct employee emp. In the main function, we create an instance of the organisation structure and initialize the emp member with an instance of the employee structure.
-
By Embedded Nested Structure: In this method, the two structures are combined into one structure. For a better understanding let’s see an example of embedded nested structure in c language.
C Program implemented by Embedded Nested Structure
#include <stdio.h> struct organisation{ char name[50]; int id; struct { char name[50]; int id; int age; } emp; }; int main(){ struct organisation org1 = {"XYZ Ltd.", 123, {"John Doe", 101, 30}}; printf("Organisation name: %s\n", org1.name); printf("Organisation ID: %d\n", org1.id); printf("Employee name: %s\n", org1.emp.name); printf("Employee ID: %d\n", org1.emp.id); printf("Employee age: %d\n", org1.emp.age); return 0; }Output
Organisation name: XYZ Ltd. Organisation ID: 123 Employee name: John Doe Employee ID: 101 Employee age: 30In this approach, the employee structure is declared inside the organization structure as an anonymous structure using the keyword struct. In the main function, we create an instance of the organization structure and initialize the emp member directly with the values of the employee structure.
Accessing Nested Structure
Nested Structure can be accessed in two ways:
- Using Normal Vriable.
- Using Pointer Variable.
- Using Normal Variable: Outer and inner structure variables are declared as normal variables and the data members of the outer structure are accessed using a single dot(.) and the data members of the inner structure are accessed using the two dots. We have already used this method in this article.
-
Using Pointer Variable: A nested structure can be accessed using a pointer variable by using a combination of dot (.) and arrow (->) operators to access the data members.
Here is an example program to illustrate how to access a nested structure using a pointer variable:
#include <stdio.h> // Declare a nested structure struct employee { char name[20]; int age; struct address { char city[20]; char state[20]; } addr; }; int main() { // Declare a pointer variable of the structure struct employee *emp_ptr; // Declare and initialize a normal variable of the structure struct employee emp = {"John", 25, {"New York", "NY"}}; // Assign the address of the normal variable to the pointer variable emp_ptr = &emp; // Access the data members of the outer structure using arrow operator printf("Name: %s\n", emp_ptr->name); printf("Age: %d\n", emp_ptr->age); // Access the data members of the inner structure using dot and arrow operators printf("City: %s\n", emp_ptr->addr.city); printf("State: %s\n", emp_ptr->addr.state); return 0; }Output
Name: John Age: 25 City: New York State: NY
Passing Structure to Function
We can pass Nested structures to functions directly by passing the structure as an argument to the function.
Code
#include <stdio.h>
struct Inner {
int x;
};
struct Outer {
int a;
int b;
struct Inner in;
};
void show(struct Outer out) {
printf("a = %d\n", out.a);
printf("b = %d\n", out.b);
printf("x = %d\n", out.in.x);
}
int main() {
struct Outer out = {1, 2, {3}};
show(out);
return 0;
} Output
a = 1
b = 2
x = 3In this example, there are two C structs Inner and Outer, where Outer contains an instance of Inner. The show function takes an instance of Outer and prints its a, b, and x values. In main, an instance of Outer is created and initialized with values 1 for a, 2 for b, and 3 for x. Then, this instance is passed as an argument to the show function. When the program is run, it prints the values of a, b, and x in the show function, which are 1, 2, and 3, respectively.
Drawbacks of Nested Structure
The drawback of nested structures are:
- Independent existence not possible: Nested structures cannot exist independently and cannot be declared as a structure variable of its own type anywhere else in the program. This means that they are limited in their use and cannot be used outside of the main structure.
- Cannot be used in multiple data structures: Nested structures cannot be used in multiple structures due to the limitation of declaring structure variables within the main structure. This can limit the flexibility and reusability of the code.
In this program, we have declared a nested structure employee that contains an inner structure address. We have then declared a pointer variable emp_ptr of the structure and a normal variable emp of the structure, and assigned the address of emp to emp_ptr.
To access the data members of the outer structure, we have used the arrow (->) operator with the pointer variable emp_ptr. To access the data members of the inner structure, we have used the dot (.) operator to access the addr member of the outer structure, and the arrow (->) operator to access the data members of the inner structure.
Overall, nested structures in C provide a powerful way to group related data together in a hierarchical manner. By understanding how to define and access nested structures, you can write more efficient and effective C code.
FAQs related to Nested Structure in C
1. What is a nested structure in C?
A nested structure is a structure type that contains one or more members of another structure type within it.
For Example
struct outer { int x; struct inner { int y; } inner_struct; };2. How do you access members of a nested structure in C?
To access members of a nested structure in C, you use the dot operator (.) to access the outer structure’s member containing the inner structure and then use another dot operator to access the inner structure’s member.
For Example
struct outer my_struct; my_struct.inner_struct.y = 10;3. Can a nested structure contain another nested structure?
Yes, a nested structure can contain another nested structure. There is no limit to the level of nesting in C structures.
4. Can you pass a nested structure to a function in C?
Yes, you can pass a nested structure to a function in C. You can pass the outer structure, which contains the inner structure, as a parameter to a function. The function can then access the inner structure’s members using the dot operator.
For Example
void my_function(struct outer my_struct) { int y = my_struct.inner_struct.y; }