What are the specific ways to improve function performance in C++?

Five ways to improve the performance of C functions: inline functions (embed code into the caller); reduce function parameter passing (only pass necessary parameters); use constant references (pass constant references of function parameters); optimize loops ( Use iterators or range loops); use local variables (access global variables or frequently obtain local variable addresses).

Specific methods to improve function performance in C

Improving function performance is the key to improving the overall performance of C programs. This article will introduce some practical ways to optimize functions to achieve better efficiency.

1. Inline functions

Inline functions embed the function code directly into the caller, eliminating the overhead of function calls. When the function body is small and called frequently, using inlining can bring significant performance improvements.

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

2. Reduce function parameters

Passing a large number of parameters to the function will increase the code size and function call overhead. Reduce the number of function parameters as much as possible and only pass necessary parameters.

// 原始函数
int sum(std::vector<int>& numbers, int start, int end) {

// 优化函数
int sum(std::vector<int>& numbers, int start = 0, int end = -1) {

3. Use constant references

const references are used to pass constant references to function parameters to avoid unnecessary copying. This is especially important for large data structures.

void print_vector(const std::vector<int>& numbers) {
  for (const int& number : numbers) {
    std::cout << number << " ";
  }
}

4. Optimize loops

Loops are a common time-consuming part of the code. Use efficient looping constructs such as iterators or range loops, and avoid unnecessary loop iterations.

// 原始循环
for (int i = 0; i < numbers.size(); i++) {
  std::cout << numbers[i] << " ";
}

// 优化循环
for (const int& number : numbers) {
  std::cout << number << " ";
}

5. Using local variables

Accessing global variables or frequently obtaining the address of local variables will cause performance degradation. Copying variables into function local variables improves access speed.

// 原始函数
int sum(const std::vector<int>& numbers) {
  int total = 0;
  for (int i = 0; i < numbers.size(); i++) {
    total += numbers[i];
  }
  return total;
}

// 优化函数
int sum(const std::vector<int>& numbers) {
  int& total = const_cast<int&>(total);
  for (int i = 0; i < numbers.size(); i++) {
    total += numbers[i];
  }
  return total;
}

Practical case

The following is an example of using inline functions to optimize code:

// 原始函数
int factorial(int n) {
  if (n == 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

// 优化函数
inline int factorial(int n) {
  if (n == 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

When compiling and running this code, after optimization The version (with inline functions) shows significant performance improvements, especially when large factorials need to be calculated.

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