Table of contents
1. The default parameters of the function
2. Function placeholder parameters
4. Function overloading - matters needing attention
1. The default parameters of the function
In C++, the formal parameters in the formal parameter list of the function can have default values
Syntax: return value type function name (parameter = default value) {}
Example 1:
#include<iostream>
using namespace std;
// 函数的默认参数
int func(int a,int b,int c)
{
return a+b+c;
}
int main()
{
func(10,20);
return 0;
}The error shows:
Fewer parameters are passed in.
Example 2:
#include<iostream>
using namespace std;
// 函数的默认参数
int func(int a,int b=20,int c=30)
{
return a+b+c;
}
int main()
{
cout<<func(10)<<endl;;
return 0;
}operation result:
Example 3:
#include<iostream>
using namespace std;
// 函数的默认参数
// 如果我们自己传入数据，就用自己的数据，如果没有，那么就用默认值
int func(int a,int b=20,int c=30)
{
return a+b+c;
}
int main()
{
cout<<func(10,40)<<endl;;
return 0;
}operation result:
Precautions:
// 1. If a position parameter has a default value, then this position must have a default value from left to right
// 2. If the function declaration has a default value, the function cannot have a default parameter when the function is implemented (only one of the declaration and the implementation has a default parameter)
Example:
#include<iostream>
using namespace std;
// 函数的默认参数
// 如果我们自己传入数据，就用自己的数据，如果没有，那么就用默认值
int func(int a,int b=20,int c=30)
{
return a+b+c;
}
int func2(int a=10,int b=10);
int func2(int a,int b)
{
return a+b;
}
int main()
{
cout<<func(10,40)<<endl;
cout<<"func2="<<func2()<<endl;
return 0;
}operation result:
2. Function placeholder parameters
The formal parameter list of a function in C++ can have a placeholder parameter, which is used as a placeholder, and the place must be filled when the function is called
Syntax: return value type function name (data type) {}
void func (int a, int) // The second parameter is for placeholder
func(10,10);// Must pass parameters to call this function
Example:
#include<iostream>
using namespace std;
// 占位参数
void func(int a,int)
{
cout<<"this is a func"<<endl;
}
// 占位参数也可以有默认值
void func2(int a,int =20)
{
cout<<"this is a func2"<<endl;
}
int main()
{
func(10,40);// 占位参数必须填补
func2(10);
return 0;
}operation result:
3. Function overloading
Function: the function name can be the same, improving reusability
Conditions to be met for function overloading:
- under the same scope
- same function name
- Function parameter types are different, or the number is different, or the order is different
Note: The return value of a function cannot be used as a condition for function overloading, nor can it have default parameters
Example:
#include<iostream>
using namespace std;
// 函数重载
void func()
{
cout<<"func函数的调用!"<<endl;
}
void func(int a,int b=10)
{
cout<<"有参数的func函数调用！"<<endl;
}
void func(double a)
{
cout<<"有参数且参数类型与上一个不同的func函数调用"<<endl;
}
void func(int a,double b)
{
cout<<"func(int a,double b)的调用"<<endl;
}
void func(double a,int b)
{
cout<<"func(double a,int b)的调用"<<endl;
}
// 注意事项
// 函数的返回值不可以作为函数重载的条件
/*int func(double a,int b)
{
cout<<"func(double a,int b)的调用"<<endl;
}*/
int main ()
{
func();
func(10);
func(3.14);
func(10,3.14);
func(3.14,10);
return 0;
}operation result:
4. Function overloading - matters needing attention
- references as overload conditions
- Function overloading encounters function default parameters
#include<iostream>
using namespace std;
// 函数重载的注意事项
//1、引用作为重载的条件
void func(int &a)
{
cout<<"func(int &a)函数的调用!"<<endl;
}
// 两个函数的区别是参数类型不同
void func(const int &a)
{
cout<<"func(const int &a)函数调用！"<<endl;
}
// 函数重载碰到默认参数的情况
void func2(int a)
{
cout<<"func2(int a)的调用"<<endl;
}
void func2(int a,int b=10)
{
cout<<"func2(int a,int b=10)的调用"<<endl;
}
int main ()
{
int a=10;
const int b=10;
func(a); // 传入一个变量的时候默认是没有const执行
func(b);
func(10);// 传入一个常量或者const修饰的变量执行的是有const修饰的函数
cout<<endl;
//func2(10);// 有默认值的时候两个函数都可以使用，有歧义，避免这样设置
func2(10);// b没有默认值的时候可以使用
func2(10,20);// 这样就很明确，即使有默认参数也不影响函数的调用
return 0;
}operation result:
