C ++类Constructor（）

Question

I have two classes: a class Complex and a class Matrix.

Isn't my constructor supposed to substitute the void arguments constructor as well? It throws an error util I declare Complex() constructor as well. g++ -std=c++14

Complex.h

class Complex {

private:
    int m_real, m_imaginary;

public:
    Complex(const int, const int);
}

complex.cpp

#include "Complex.h"

// Constructor
Complex::Complex(const int real = 0, const int img = 0) : m_real(real), m_imaginary(img) { }

Matrix.h

class Complex;

class Matrix {

private:
    int m_lines, m_columns;
    Complex *m_matrix;

public:
    Matrix(const int, const int, const Complex &);
}

matrix.cpp

#include "Matrix.h"
#include "Complex.h"

Matrix::Matrix(const int nr_lines, const int nr_columns, const Complex &comp) : m_lines(nr_lines), m_columns(nr_columns) {
    m_matrix = new Complex[nr_lines * nr_columns];
    some other code goes here...

|7|error: no matching function for call to 'Complex::Complex()'|

Answer 1

Same here - I tested the code I wrote based on your description. It compiles and runs just fine on VS2015, VS2017.

class Complex
{
private:
   int m_real;
   int m_img;

public:
   Complex(const int real = 0, const int img = 0) 
      : m_real(real)
      , m_img(img)
   {

   }
};

class Matrix
{
private:
   Complex* matrix;

public:
   Matrix(int nr_lines = 3, int nr_columns = 3)
   {
      matrix = new Complex[nr_lines * nr_columns];
   }

   ~Matrix()
   {
      delete[] matrix;
   }
};

int main()
{
   Matrix* t = new Matrix();
   return 1;
}

Answer 2

It seems your error is somewhere else. As Some programmer dude pointed out, you could have figured this out with a minimal, complete and verifiable example - https://stackoverflow.com/help/mcve

I created a small example:

#include <iostream>
#include <stdlib.h>

class Complex {
    private:
        int m_n;
        int m_i;

    public:
        Complex (const int n = 0, const int i = 0) : m_n (n), m_i (i) {
            std::cout << "Complex ctor: " << n << ", " << i << std::endl;
        };
};

int main(int argc, char** argv) {
    int cnt = 12;
    if (argc > 1)
        cnt = atoi (argv[1]);
    Complex* m = new Complex[cnt];
    (void)m; //no warning for unused variable
    return 0;
}

Building with g++ and running:

pan:~$ g++ example.cpp -Wall -o example.elf
pan:~$ ./example.elf 4
Complex ctor: 0, 0
Complex ctor: 0, 0
Complex ctor: 0, 0
Complex ctor: 0, 0
pan:~$

As you can see, this C++ class constructor works well & as expected .

My gcc is g++ (SUSE Linux) 4.8.5 .