How to use variable length parameters of C++ functions?

Variable parameter functions in C allow receiving a variable number of parameters. The syntax is: returntype function_name(type1 arg1, type2 arg2, ..., typen argn);. When calling a variable-length parameter function, use the form function_name(arg1, arg2, ..., argn);, where arg1 to argn are the actual parameters passed. As shown in the actual case, the function sum that calculates the sum of a list of numbers uses va_list to traverse and accumulate variable-length parameters to achieve the function of dynamically obtaining parameters and calculating.

C Variable-length parameters of the function

Variable parameters allow the function to receive a variable number of parameters. In C, use the ... (ellipsis) syntax to specify variable-length arguments.

Syntax

returntype function_name(type1 arg1, type2 arg2, ..., typen argn);

Among them, returntype is the return value type of the function, arg1, arg2, ..., argn is the function parameter list, ... represents variable length parameters.

Calling

When calling a variable-length parameter function, you can use the following form:

function_name(arg1, arg2, ..., argn);

where, arg1, arg2, ..., argn are the parameters actually passed to the function.

Practical case

Here is an example of a function that calculates the sum of a given list of numbers:

#include <iostream>
#include <stdarg.h>

using namespace std;

// 计算数字列表和的函数
int sum(int num, ...) {
  va_list args;
  int sum = num;

  // 获取变长参数
  va_start(args, num);

  // 遍历变长参数并累加
  while (int arg = va_arg(args, int)) {
    sum += arg;
  }

  // 清理变长参数
  va_end(args);

  return sum;
}

int main() {
  // 调用函数计算数字列表和
  cout << "数字列表和为：" << sum(1, 2, 3, 4, 5) << endl;

  return 0;
}

Output

数字列表和为：15

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