How to define and call variadic functions in C++?

In C, use... (ellipsis) to define a variable parameter function, allowing the function to accept any number of parameters; when calling, just treat it as a fixed parameter function.

#How to define and call variadic functions in C?

Variadic functions (also known as variadic functions) allow functions to accept any number of parameters. The C standard library contains a series of variadic functions, such as printf() and scanf(). You can also define your own variadic functions.

Define a variadic function

To define a variadic function, use the syntax ... (ellipsis). It means that the function can take any number of parameters. For example:

#include <iostream>
#include <cstdarg> // 包含 va_list 和相关的宏

void print_numbers(int count, ...) {
  va_list args;
  va_start(args, count); // 初始化 va_list 对象

  // 遍历可变参数
  for (int i = 0; i < count; i++) {
    int num = va_arg(args, int); // 获取下一个 int 类型的参数
    std::cout << num << " ";
  }

  va_end(args); // 清理 va_list 对象
}

Note that ... must be placed after all fixed parameter definitions.

Calling a variadic function

To call a variadic function, simply treat it as another function with a fixed number of arguments. For example:

print_numbers(3, 1, 2, 3);

This function will print out 1 2 3.

Practical case

The following example demonstrates how to define and call a variable parameter function:

#include <iostream>

void print_max(int count, ...) {
  va_list args;
  va_start(args, count);

  // 保存最大值
  int max = INT_MIN;

  // 获取并比较可变参数
  for (int i = 0; i < count; i++) {
    int num = va_arg(args, int);
    if (num > max) {
      max = num;
    }
  }

  va_end(args);

  // 打印最大值
  std::cout << "最大值：" << max << std::endl;
}

int main() {
  print_max(3, 1, 2, 3);
  print_max(5, 3, 5, 2, 1, 7);

  return 0;
}

Output:

最大值：3
最大值：7

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