How to Declare a Struct Inside a Struct in C?

A structure is a composite data type in C programming that enables combining several data types under one name. A structure inside a structure is also called a nested structure. In this article, we will learn how to declare a structure inside a structure in C++.

Declare a Struct Inside a Struct in C

To declare a structure inside a structure, we need to first define the inner structure(the structure that we want to nest inside another structure) and then define the outer struct and include the inner struct as a member using the below syntax:

Syntax to Declare Nested Structure

struct innerStructName {
     //define inner structure
};

struct outerStructName {
    struct innerStructName st; // inner struct as Direct member
};

We can also declare it directly inside the parent structure:

struct outerStructName {
    struct innerStructName {
       //define inner structure
    };
};

C Program to Declare Struct Inside a Struct

The below program demonstrates how we can declare a nested structure and use it in C.

C

// C program to declare a structure inside a structure
#include <stdio.h>

// Declaring the inner struct
struct InnerStruct {
    char innerChar;
    float innerFloat;
};

// Declaring the outer struct
struct OuterStruct {
    int outerData;
    struct InnerStruct inner;
};

int main()
{
    // Creating an instance of the outer struct
    struct OuterStruct myStruct;

    // Accessing and modifying the members of the inner
    // struct
    myStruct.inner.innerChar = 'X';
    myStruct.inner.innerFloat = 5.14;

    // Accessing the members of both the outer and
    // inner structs
    printf("Outer Data: %d\n", myStruct.outerData);
    printf("Inner Char: %c\n", myStruct.inner.innerChar);
    printf("Inner Float: %.2f\n",
           myStruct.inner.innerFloat);

    return 0;
}

Output

Outer Data: 0
Inner Char: X
Inner Float: 5.14