What is the purpose of function inlining in C++?

Function inlining is an optimization technology that embeds the function body directly into the call point, eliminating function call overhead and improving program execution efficiency. It works well for small functions, reducing code size and improving code readability.

The purpose of function inlining in C

Function inlining is a method of embedding the function body directly into the call point, and Rather than using the usual optimization techniques of the function call mechanism. It can improve program execution efficiency by eliminating function call overhead.

Syntax:

inline 返回值类型 函数名(参数列表) {
  // 函数体
}

Advantages:

• Eliminate function call overhead: Linked functions are expanded at the call site at compile time, eliminating the overhead of function calls and returns.
• Reduce code size: Inline function bodies will not be executed repeatedly in the final executable file, thereby reducing code size.
• Improve code readability: Inline functions appear directly at the call point, making the code easier to understand and maintain.

Practical Example:

Consider the following example:

int fibonacci(int n) {
  if (n <= 1) {
    return n;
  }
  return fibonacci(n - 1) + fibonacci(n - 2);
}

int main() {
  int result = fibonacci(10);
  return 0;
}

This example calculates the 10th term of the Fibonacci sequence. Function fibonacci is recursive, which will result in a large number of function calls, thus reducing performance.

We can optimize the function by making it inline:

inline int fibonacci(int n) {
  if (n <= 1) {
    return n;
  }
  return fibonacci(n - 1) + fibonacci(n - 2);
}

The compiler will insert the code of the fibonacci function directly into the main function , thus eliminating the overhead of recursive calls. This will significantly improve program execution efficiency.

Note:

• Not all functions are suitable for inlining. Small functions are often good candidates for inlining.
• Excessive use of function inlining can increase the size of the executable file. Choose carefully which functions to inline.

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