🔗 C Structures and Functions – Passing and Returning Structures in C

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🧲 Introduction – How Do Structures Interact with Functions?

In C programming, structures can be passed to functions and returned from functions, just like any other data type. This enables powerful and organized code for manipulating records, objects, or grouped variables within modular logic.

🎯 In this guide, you’ll learn:

• How to pass structures to functions (by value and pointer)
• How to return structures from functions
• Practical examples for manipulating structured data
• Best practices and performance tips

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🔍 Core Concept – Pass by Value vs Pass by Pointer

Method	Behavior
Pass by Value	Copies the structure into the function
Pass by Pointer	Passes the memory address (reference)

🔁 Pass-by-pointer allows the function to modify the original structure, while pass-by-value only modifies a copy.

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💻 Code Examples – Using Structures with Functions

✅ Example 1: Passing Structure by Value

#include <stdio.h>

struct Student {
    char name[50];
    float marks;
};

void display(struct Student s) {
    printf("Name: %s, Marks: %.2f\n", s.name, s.marks);
}

int main() {
    struct Student s1 = {"Alice", 88.5};
    display(s1);  // Pass by value
    return 0;
}

📘 This method is simple but can be inefficient for large structures.

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✅ Example 2: Passing Structure by Pointer

#include <stdio.h>

struct Student {
    char name[50];
    float marks;
};

void updateMarks(struct Student *s, float newMarks) {
    s->marks = newMarks;  // Modify original structure
}

int main() {
    struct Student s1 = {"Bob", 72.0};
    updateMarks(&s1, 95.0);  // Pass by pointer
    printf("Updated Marks: %.2f\n", s1.marks);
    return 0;
}

📌 Use the arrow operator (->) to access structure members via pointer.

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✅ Example 3: Returning a Structure from a Function

#include <stdio.h>

struct Point {
    int x, y;
};

struct Point createPoint(int x, int y) {
    struct Point p = {x, y};
    return p;  // Return entire structure
}

int main() {
    struct Point pt = createPoint(5, 10);
    printf("Point: (%d, %d)\n", pt.x, pt.y);
    return 0;
}

📌 Entire structure is returned by value. Avoid this for large structures unless necessary.

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📚 Use Cases

Use Case	Example
Displaying details	display(struct Employee e)
Updating fields	update(struct *e)
Constructing objects	createStruct() returns struct
Initializing from user input	inputStudent(struct *s)

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💡 Best Practices & Tips

📘 Best Practice:
Use pointers to pass structures when performance or modification is required.

💡 Tip:
Combine with typedef to simplify syntax:

typedef struct {
    char title[50];
    int pages;
} Book;

void print(Book b);  // Easier than struct Book

⚠️ Pitfall:
Returning a pointer to a local structure variable leads to dangling pointer errors.

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🛠️ Real-World Applications

• 📊 Passing Student, Employee, Order structures between modules
• 🧪 Creating configuration/data objects on the fly
• 🔧 Embedded systems passing sensor/command structs
• 🧠 Struct-based message and packet handling

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📌 Summary – Recap & Next Steps

Structures in C can be passed to or returned from functions, enabling better abstraction and cleaner code. Choose between passing by value or pointer based on memory and performance needs.

🔍 Key Takeaways:

• Structures can be passed and returned like primitive types
• Use pointers to avoid copying and enable modification
• Use typedef to simplify function declarations
• Avoid returning pointers to local structure variables

⚙️ Real-World Relevance:

Essential for modular C applications, embedded firmware, data processing, and custom libraries.

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❓ Frequently Asked Questions (FAQ)

❓ Can I pass a structure to a function?

✅ Yes. You can pass it by value (copy) or by pointer (reference).

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❓ How do I modify a structure inside a function?

✅ Pass it by pointer and use the -> operator to modify its members.

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❓ Can I return a structure from a function?

✅ Yes. Entire structures can be returned by value, although large structures may impact performance.

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❓ What’s the advantage of using typedef with structures?

✅ It reduces verbosity and simplifies syntax in function prototypes and definitions.

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❓ Why is passing a structure pointer more efficient?

✅ Because it passes just the address (usually 4–8 bytes), not a full copy of the data.

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