C ++没有匹配的调用函数

Question

I have error: No matching function for call to 'Goo::Goo()'

This problem is happening to often, can somebady explain to me where do i make mistakes all the time. I How can i overcome this.

Here is the code of the progam:

#include <iostream>

using namespace std;

class Goo{
  private:
    int a[10];
    int n;

  public:
    Goo(int x){
        n=x;
    }

    Goo(const Goo &g){
        this->n=g.n;
        for(int i=0;i<g.n;i++){
            this->a[i]=g.n;
        }
    }

    Goo operator=(const Goo &g){
        this->n=g.n;
        for(int i=0;i<g.n;i++){
            this->a[i]=g.n;
        }
        return *this;
    }

    Goo operator+(const Goo &g){
        Goo goo;
        for(int i=0;i<g.n;i++){
            goo.a[i]=this->a[i]+g.a[i];
        }
        return goo;
    }

    friend istream& operator>>(istream &in,Goo &g){
        in>>g.n;
        for(int i=0;i<g.n;i++){
            in>>g.a[i];
        }
        return in;
    }

    friend ostream& operator<<(ostream &out,Goo &g){
        for(int i=0;i<g.n;i++){
            out<<g.a[i]<<" ";
        }
        return out;
    }
};

int main()
{
   Goo A,B;

   cin>>A>>B;

   Goo C=A+B;

   cout<<C;
   return 0;
}

Answer 1

When you define a custom constructor (among other reasons ), the class no longer has a default constructor:

struct Foo {
    int x;
};
Foo foo;  // OK

struct Foo {
    int x;
    Foo(int x_) : x{x_} { }
};
Foo foo;  // error

You can fix this by either adding a custom default constructor:

struct Foo {
    int x;
    Foo() { }
    Foo(int x_) : x{x_} { }
};

or having at least one constructor with all default parameters:

struct Foo {
    int x;
    Foo(int x_ = 0) : x{x_} { }
};

Since C++11, you can also force the compiler to emit the default constructor:

struct Foo {
    int x;
    Foo() = default;
    Foo(int x_ = 0) : x{x_} { }
};