Detailed explanation of default parameters and variable parameters of C++ functions

C Default parameters allow setting default values ​​for function parameters, while in variadic parameters, any number of parameters can be provided to the function. Specifically: Default parameters: Allows specifying default values ​​for parameters when the function is declared, and using the default value if no value is provided when calling. Variable parameters: Use... to indicate that the function can accept any number of parameters and obtain the parameters through va_arg.

#Detailed explanation of default parameters and variable parameters of C function

Default parameters

Default parameters allow us to specify parameters when the function is declared a default value. This way, when the function is called, if no value is provided for the parameter, the default value is used.

Syntax:

return_type function_name(parameter_type1 parameter_name1 = default_value1,
                       parameter_type2 parameter_name2 = default_value2,
                       ...);

Practical case:

Consider the following function, which has a default max_size Parameters:

int get_max_size(int max_size = 100) {
  // 函数体
  return max_size;
}

This function can be called as follows:

int size1 = get_max_size(); // 使用默认值 100
int size2 = get_max_size(50); // 使用给定值 50

Variadic parameters

Variadic parameters allow us to provide any number of parameters to the function. In function declarations, variable parameters are represented using ....

Syntax:

return_type function_name(parameter_type1 parameter_name1,
                       parameter_type2 parameter_name2,
                       ...,
                       parameter_typeN ...parameter_nameN);

Practical example:

Consider the following function, which calculates the sum of any number of numbers:

int sum(int num, ...) {
  int sum = num;
  
  va_list args;
  va_start(args, num);
  
  while (true) {
    int n = va_arg(args, int);  // 获取下一个参数
    if (n == 0) {
      break;
    }
    sum += n;
  }
  
  va_end(args);
  return sum;
}

This The function can be called as follows:

int sum1 = sum(1, 2, 3, 4, 5); // 求和 1 + 2 + 3 + 4 + 5 = 15
int sum2 = sum(10, 20, 30, 0); // 求和 10 + 20 + 30 = 60

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