C++ function call optimization: efficient strategies for parameter passing and return values

C Function call optimization strategy includes: 1. Parameter passing: passing by reference to modify the original value; 2. const parameters: preventing parameter modification and copying; 3. Return value: returning a large data structure by reference, saving copy overhead ;4. Return rvalue reference to avoid unnecessary copying. Through these strategies, function call performance can be optimized and program efficiency improved.

#C Function Call Optimization: Efficient Strategies for Parameter Passing and Return Values

In C programming, function calls are a common part of program execution. Optimizing function calls can improve the overall performance of the program. This article will introduce several parameter passing and return value optimization strategies and demonstrate them with code examples.

Parameter passing optimization

Method 1: Pass by value vs. Pass by reference

• Pass by value: Copying the parameter value and passing it to the function is expensive.
• Pass by reference: Pass the reference of the parameter. Modifying the parameter value in the function will modify the original value.

When you need to modify the parameter value in the function, using pass by reference can avoid parameter copy overhead, for example:

void Swap(int& a, int& b) {
  int temp = a;
  a = b;
  b = temp;
}

Method 2: const parameter

is a function Parameter declaration as const can prevent the function from modifying the parameter value and avoid unnecessary copying, for example:

int Max(const int& a, const int& b) {
  return a > b ? a : b;
}

Return value optimization

Method 1: Return by value vs. Return by reference

• Return by value: Copy the return value.
• Return by reference: Return the reference of the return value. Modifying the reference value will modify the original value.

For large data structures, returning by reference can save copy overhead, for example:

std::vector<int>& GetVector() {
  static std::vector<int> v = {1, 2, 3};
  return v;
}

Method 2: Return rvalue reference

For instant creation and no longer used Objects can avoid unnecessary copying, for example:

std::string Concatenate(const std::string& a, const std::string& b) {
  return a + b;
}

Practical case

Function call optimization

#include <iostream>

void OptimizedSwap(int& a, int& b) {
  a ^= b;
  b ^= a;
  a ^= b;
}

int main() {
  int x = 1, y = 2;
  OptimizedSwap(x, y);
  std::cout << "x: " << x << ", y: " << y << std::endl;  // 输出: x: 2, y: 1

  return 0;
}

In this example, OptimizedSwap function Use bitwise operations to swap the values ​​of two integers, avoiding the overhead of variable copying.

Return value optimization

#include <iostream>

std::vector<int>& OptimizedGetVector() {
  static std::vector<int> v = {1, 2, 3};
  return v;
}

int main() {
  auto& v = GetVector();  // 按引用获得 vector
  v.push_back(4);

  for (int i : v) {
    std::cout << i << " ";  // 输出: 1 2 3 4
  }
  std::cout << std::endl;

  return 0;
}

In this example, the OptimizedGetVector function returns a std::vector by reference, avoiding the overhead of creating a new vector. .

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