Function default parameters, function placeholder parameters, function overloading and precautions

stay C++ in , The parameters in the function's parameter list can have default values

grammar ： return type Function name （ Parameters = The default value is ）{ }

#include<iostream>

usingnamespace std;

// If we pass in parameters ourselves , Just use your own data , without , Then use the default value

int func(inta, intb=20, intc=30)

{

    returna + b + c;

}

// matters needing attention

//1. If a location already has default parameters , So back from this position , There must be default values from left to right

//int func2(int a = 10, int b, int c)  That's the wrong way to write it ！

//{

//  return a + b + c;

//}

//2. If the function declaration has default arguments , Function implementations cannot have default parameters

// Declaration and implementation can only have one default parameter

//int func3(int a, int b = 20, int c = 30); That's the wrong way to write it ！

//int func3(int a, int b = 20, int c = 30)

//{

//  return a + b + c;

//}

int main()

{

    cout << func(10,30) << endl;

    system("pause");

    return 0;

}

2. Function space occupying parameter

C++ There can be space occupying parameters in the formal parameter list of functions in , For space occupying , This position must be filled when the function is called

grammar ： return type Function name （ data type ）{ }

#include<iostream>

usingnamespace std;

// Placeholder parameters

// The placeholder parameter can also have a default parameter // If there is a default value, it is useless

void func(inta, int)

{

    cout <<"helloworld"<< endl;

}

int main()

{

    func(10,34);

    system("pause");

    return 0;

}

3. function overloading

effect ： Function names can be the same , Improve reusability

Function overload satisfies the condition ：

1. Under the same scope

2. Same function name

3. Function parameter Different types perhaps The number is different. perhaps Different order

Be careful ： The return value of a function cannot be used as a condition for overloading a function

#include<iostream>

usingnamespace std;

void func()

{

    cout <<"helloworld"<< endl;

}

void func(inta)

{

    cout <<a<< endl;

}

void func(doubleb)

{

    cout <<b<< endl;

}

void func(doubleb, intc)

{

    cout <<b<<"  "<<c<< endl;

}

int main()

{

    func();

    func(19);

    func(6.34);

    func(3.14, 3);

    system("pause");

    return 0;

}

4. Function overload considerations

Reference as overload condition

Function overload encountered function default parameter

#include<iostream>

usingnamespace std;

void func(int& a)//int &a=10; illegal

{

    cout <<"int &a call "<<endl;

}

void func(constint& a)//const int &a=10 legal

{

    cout <<"const int &a call "<< endl;

}

void func2(inta,intb=10)

{

    cout <<"func2 int a,int b=10 Call to "<< endl;

}

void func2(inta)

{

    cout <<"func2 int a Call to "<< endl;

}

int main()

{

    int a = 10;

    func(a);// Adjust the first

    func(10);// Tune the second

    func2(10);// When a function overload encounters a default parameter , There is ambiguity , Will report a mistake , The third and fourth functions do not know which one to call

}