Inline Functions in C++

Inline functions replace function calls with actual code at compile time, eliminating overhead.

Use 'inline' keyword for small, frequently called functions like getters/setters.

Compiler decides if inlining happens; it's a hint, not a command.

1. Why Use Inline Functions?

Normal calls: push parameters, jump, stack setup (overhead).

Inline: Code copied directly—no jump.

Benefits: Faster execution for tiny functions.

Drawbacks: Larger executable size.

2. Syntax and Declaration

inline int max(int a, int b) {
    return (a > b) ? a : b;
}

Declare in header (.h); definition must be visible.

3. Simple Example

#include <iostream>
using namespace std;

inline int getSum(int a, int b) {
    return a + b;
}

int main() {
    cout << getSum(5, 3) << endl;  // Expands to 5+3
    return 0;
}

Output: 8. Compiler replaces call with code.

4. Inline in Classes

Member functions defined inside class are auto-inline.

class Rectangle {
public:
    int width, height;
    int area() { return width * height; }  // Inline
};

5. When Compiler Ignores Inline

- Loops, recursion, switch.

- Static variables.

- Functions > ~10 lines.

6. Macros vs Inline Functions

Macros: Text replacement (unsafe).

#define SQUARE(x) ((x)*(x))  // Macro
inline int square(int x) { return x * x; }  // Safe

Inline: Type-safe, no side-effect issues.

7. Best Practices

- Small/simple functions only.

- In headers for templates/classes.

- Profile before/after—don't assume speedup.

Conclusion

Inline functions optimize performance-critical code.

Use wisely; modern compilers inline smartly anyway.