Passing Structures to Functions

You can pass a structure to a function the same way you pass any variable. There are three approaches:

Pass by Value
Pass by Reference (using pointer)
Return a structure from a function

1. Pass by Value

A copy of the structure is sent to the function. Changes made inside the function do not affect the original.

#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

void display(struct Student s) {
    s.marks = 99.9f;   // modifies only the local copy
    printf("Inside : %s %d %.2f\n", s.name, s.roll, s.marks);
}

int main() {
    struct Student s1 = {"Vishal", 101, 75.5};
    display(s1);
    printf("Outside: %.2f\n", s1.marks);   // original unchanged
    return 0;
}

Output:

Inside : Vishal 101 99.90
Outside: 75.50

2. Pass by Reference (Using Pointer)

The address of the structure is sent. Changes made inside the function do affect the original. Members are accessed using the arrow operator (->).

#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

void update(struct Student *s) {
    s->marks = 99.9f;   // modifies the original
}

int main() {
    struct Student s1 = {"Vishal", 101, 75.5};
    update(&s1);   // pass address
    printf("After update: %.2f\n", s1.marks);
    return 0;
}

Output:

After update: 99.90

3. Return a Structure from a Function

#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

struct Student getData() {
    struct Student s = {"Kumar", 102, 80.5};
    return s;
}

int main() {
    struct Student s1 = getData();
    printf("%s - %d - %.2f\n", s1.name, s1.roll, s1.marks);
    return 0;
}
// Output: Kumar - 102 - 80.50

Comparison

Method	Copies Data	Modifies Original	Speed
Pass by Value	Yes	No	Slower
Pass by Reference	No	Yes	Faster
Return struct	Yes	—	Moderate

Best practice: For large structures, always prefer passing by reference using a pointer. Use const struct Type *ptr if you want to read without modifying.

Fundamentals

Functions

Array

String

Structure

Union

Pointer

File Handling

Preprocessor

Passing Structures to Functions

Passing Structures to Functions

1. Pass by Value

2. Pass by Reference (Using Pointer)

3. Return a Structure from a Function

Comparison

​Passing Structures to Functions

​1. Pass by Value

​2. Pass by Reference (Using Pointer)

​3. Return a Structure from a Function

​Comparison

Passing Structures to Functions

1. Pass by Value

2. Pass by Reference (Using Pointer)

3. Return a Structure from a Function

Comparison