How to optimize the use of default parameters and variadic parameters in C++ functions

Optimize C default and variable parameter functions: Default parameters: Allow functions to use default values ​​to reduce redundancy. Put default parameters last to improve readability. Use constexpr default parameters to reduce overhead. Use structured binding to improve readability of complex default parameters. Variable parameters: allows a function to accept a variable number of parameters. Try to avoid using variadic arguments and use them only when necessary. Optimize variadic functions using std::initializer_list to improve performance.

Optimize the use of default parameters and variable parameters in C functions

Default parameters

Default parameters allow functions to use default values ​​when specific parameters are not provided. This helps reduce redundant code in function calls. For example:

int add(int a, int b = 0) {
  return a + b;
}

int main() {
  cout << add(1) << endl; // 输出 1
  cout << add(1, 2) << endl; // 输出 3
}

Variadic parameters

Variadic parameters allow a function to accept a variable number of parameters. This is useful for functions that need to handle an unknown number of arguments. For example:

int sum(int num, ...) {
  va_list args;
  va_start(args, num);

  int sum = num;
  int arg;
  while ((arg = va_arg(args, int)) != 0) {
    sum += arg;
  }

  va_end(args);
  return sum;
}

int main() {
  cout << sum(1) << endl; // 输出 1
  cout << sum(1, 2, 3, 4, 5) << endl; // 输出 15
}

Optimization tips

• Try to avoid using variable parameters: Variable parameters will introduce performance overhead, so only when Use them only when necessary.
• Place default parameters at the end: Placing default parameters at the end of the function parameter list can improve readability and maintainability.
• Use constexpr default parameters: If the default value is known and will not change, using the constexpr modifier can reduce overhead.
• Use structured binding: For complex default parameters, you can use structured binding to create more readable code.

Practical case:

Variable parameter optimization:

// 旧版：存在性能开销
int max(int num, ...) {
  va_list args;
  va_start(args, num);

  int max = num;
  int arg;
  while ((arg = va_arg(args, int)) != 0) {
    max = std::max(max, arg);
  }

  va_end(args);
  return max;
}

// 新版：使用 std::initializer_list 优化
int max(int num, std::initializer_list<int> args) {
  return *std::max_element(args.begin(), args.end(), [](int a, int b) { return a > b; });
}

Default parameter optimization:

// 旧版：默认值不在最后，可读性差
int add(int b, int a = 0) {
  return a + b;
}

// 新版：默认值在最后，可读性好
int add(int a, int b = 0) {
  return a + b;
}

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