How to choose the right function to be inlined

Criteria for selecting inline functions: The function body is small (less than 10 lines of code), frequently called, no side effects, closely related to the calling location, code size is not sensitive

How to choose a suitable function as an inline function

Introduction
Inline functions are an optimization technique that allows you to embed the function body directly into the caller code to improve performance. However, not all functions are suitable as inline functions. This article will explore how to choose the right function to be inlined.

Advantages of inline functions

• # Faster code execution: Inline functions eliminate the overhead of function calls and returns, thereby increasing execution speed.
• Smaller code size: Inline functions require no additional function call instructions and therefore can reduce code size.
• Better code readability: Inline functions embed function logic into the code that calls it, making the code easier to understand and maintain.

Disadvantages of inline functions

• Larger code size: Inlining large functions can cause significant code size increasing.
• Harder to debug: Inline functions make it difficult to trace the code execution flow because the function body is scattered in multiple locations.
• Potential code redundancy: If the same function is called multiple times, inlining will lead to code redundancy and waste memory space.

Guidelines for selecting inline functions

• Small function body: Small function body (usually less than 10 lines code) is suitable for inlining.
• Frequently called: Frequently called functions can benefit from inlining.
• Side-effect-free: Side-effect-free functions do not affect the state of the calling function, which makes them ideal candidates for inlining.
• Closely related to the calling location: Functions closely related to the calling location, such as local helper functions, are suitable for inlining.
• Code Size Insensitivity: For applications that are not code size sensitive, inlining large functions may also be feasible.

Practical case
The following is a C code example that uses the square function as an inline function:

#include <iostream>

// 将平方函数作为内联函数
inline int square(int x) { return x * x; }

int main() {
  int number = 5;
  std::cout << "平方值为：" << square(number) << std::endl;
  return 0;
}

In this example, The square function is a small, frequently called function that is closely related to the code that calls it. Making it an inline function improves code execution speed and readability.

Conclusion
By following the guidelines outlined in this article, you can choose the appropriate function to inline. Inline functions can improve code performance and readability, but must be used with caution to avoid code redundancy and larger code size.

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