INLINE FUNCTION IN C++

                                                        Inline function

An inline function is a function for which the compiler replaces the function call with the actual function code at compile time.

 

Usability of Inline Functions

Problem with Normal Functions

Normal function calls cause:

• Function call overhead
• Stack memory usage
• Slower execution for small functions

Inline Function

Inline functions:

• Improve execution speed
• Reduce function call overhead
• Suitable for small and frequently used functions

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Syntax of Inline Function

inline return_type function_name(parameters)

{

    // function body

}

 

Example : Inline Function to Add Two Numbers

#include <iostream>

using namespace std;

 

inline int add(int a, int b)

{

    return a + b;

}

 

int main()

{

    int x = 10, y = 20;

    cout << "Sum = " << add(x, y);

    return 0;

}

 

Process of Compiler Handles Inline Functions

Even if a function is declared inline:

• The compiler may ignore it
• Inline is only a request, not a command

 

Compiler may NOT inline if:

• The function is large
• Uses loops
• Uses recursion
• Uses static variables
• Function complexity is high

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Inline Function with Class

All functions defined inside a class are implicitly inline.

 

Example: Inline Function Inside Class

#include <iostream>

using namespace std;

 

class Demo

{

public:

    inline void show()

    {

        cout << "This is an inline member function";

    }

};

 

int main()

{

    Demo d;

    d.show();

    return 0;

}

 

---

Inline Function Defined Outside Class

 

Example

#include <iostream>

using namespace std;

 

class Sample

{

public:

    void display();

};

 

inline void Sample::display()

{

    cout << "Inline function outside class";

}

 

int main()

{

    Sample s;

    s.display();

    return 0;

}

---

Inline Function with Default Arguments

#include <iostream>

using namespace std;

 

inline int multiply(int a, int b = 2)

{

    return a * b;

}

 

int main()

{

    cout << multiply(5) << endl;

    cout << multiply(5, 3);

    return 0;

}

---

 

Advantages of Inline Functions

Faster execution
No function call overhead
Type safety
Better debugging
More readable than macros

---

 

Disadvantages of Inline Functions

Increases program size
Not suitable for large functions

The compiler may ignore it

---

When to Use Inline Functions?

✔ Small functions
✔ Frequently called functions
✔ Simple logic (1–3 lines)

 

 Avoid for:

• Recursive functions
• Large code blocks
• Complex logic

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