Using a classes object with constructor in another class. error : no matching function for call

Question

错误信息如下： main.cpp|119|error: no matching function for call to 'Matrix2D::Matrix2D()'|

我的猜测是，当在 class NeuralNewtork 中声明 Matrix2D first_hidden_weights 时，它需要 2 个参数，因为 class Matrix2D-s 构造函数。但是我不能给它参数，因为我还不知道它们。

#include <stdlib.h>
#include <time.h>
#include <vector>

using namespace std;

float RandomNumber()
{
    return ((((double) rand() / (RAND_MAX))*2)-1);
}

class Matrix2D{
    public:
        int rows;
        int columns;
        vector<vector<float> > matrix;
        Matrix2D(int x, int y){
            rows = x;
            columns = y;
            for (int i = 0; i < rows; i++) {
                vector<float> v1;
                for (int j = 0; j < columns; j++) {
                    v1.push_back(0);
                }
                matrix.push_back(v1);
            }
        }
        Matrix2D randomizeMatrix(){
            Matrix2D result(rows, columns);
            for (int i = 0; i < rows; i++) {
                for (int j = 0; j < columns; j++) {
                    matrix[i][j] = RandomNumber();
                }
            }
            return result;
        }
        static Matrix2D scalarMultiply(Matrix2D x, float y){
            Matrix2D result(x.rows, x.columns);
            for (int i = 0; i < x.rows; i++) {
                for (int j = 0; j < x.columns; j++) {
                    result.matrix[i][j] = x.matrix[i][j] * y;
                }
            }
            return result;
        }
        static Matrix2D scalarAddition(Matrix2D x, float y){
            Matrix2D result(x.rows, x.columns);
            for (int i = 0; i < x.rows; i++) {
                for (int j = 0; j < x.columns; j++) {
                    result.matrix[i][j] = x.matrix[i][j] + y;
                }
            }
            return result;
        }
        static Matrix2D scalarSubstraction(Matrix2D x, float y){
            Matrix2D result(x.rows, x.columns);
            for (int i = 0; i < x.rows; i++) {
                for (int j = 0; j < x.columns; j++) {
                    result.matrix[i][j] = x.matrix[i][j] - y;
                }
            }
            return result;
        }
        static Matrix2D matrixAddition(Matrix2D x, Matrix2D y){
            Matrix2D result(x.rows, x.columns);
            for (int i = 0; i < x.rows; i++) {
                for (int j = 0; j < x.columns; j++) {
                    result.matrix[i][j] = x.matrix[i][j] + y.matrix[i][j];
                }
            }
            return result;
        }
        static Matrix2D matrixTranspose(Matrix2D x){
            Matrix2D result(x.columns, x.rows);
            for (int i = 0; i < x.rows; i++) {
                for (int j = 0; j < x.columns; j++) {
                    result.matrix[j][i] = x.matrix[i][j];
                }
            }
            return result;
        }
        static Matrix2D matrixMultiplication(Matrix2D x, Matrix2D y){
            Matrix2D result(x.rows, y.columns);
            for (int i = 0; i < result.rows; i++) {
                for (int j = 0; j < result.columns; j++) {
                    float sum = 0;
                    for (int k = 0; k < x.columns; i++) {
                        sum += x.matrix[i][k] * y.matrix[k][j];
                    }
                    result.matrix[i][j] = sum;
                }
            }
            return result;
        }
        void printMatrix(){
            for (int i = 0; i < rows; i++) {
                for (int j = 0; j < columns; j++) {
                cout << matrix[i][j] << " ";
                }
            cout << endl;
            }
            cout << endl;
        }
};

class NeuralNewtork{
    public:
        int numberof_input_nodes;
        int numberof_hidden_layers;
        int numberof_hidden_nodes;
        int numberof_output_nodes;
        Matrix2D first_hidden_weights;
        vector<Matrix2D> hidden_weights;
        Matrix2D output_weights;
        vector<Matrix2D> hidden_biases;
        Matrix2D output_biases;

        NeuralNewtork(int input_nodes, int hidden_layers, int hidden_nodes, int output_nodes){ // This line
               //gives 3 errors, all of them the same.
            numberof_input_nodes = input_nodes;
            numberof_hidden_layers = hidden_layers;
            numberof_hidden_nodes = hidden_nodes;
            numberof_output_nodes = output_nodes;

            first_hidden_weights = Matrix2D(numberof_hidden_nodes, numberof_input_nodes);
            first_hidden_weights.randomizeMatrix();

            hidden_weights.reserve(numberof_hidden_layers-1);
            for (int i=0; i<numberof_hidden_layers-1; i++){
                hidden_weights.push_back(Matrix2D(numberof_hidden_nodes, numberof_hidden_nodes));
                hidden_weights.back().randomizeMatrix();
            }

            output_weights = Matrix2D(numberof_output_nodes, numberof_hidden_nodes);
            output_weights.randomizeMatrix();

            hidden_biases.reserve(numberof_hidden_layers);
            for (int i=0; i<numberof_hidden_layers; i++){
                hidden_biases.push_back(Matrix2D(numberof_hidden_nodes, 1));
                hidden_biases.back().randomizeMatrix();
            }

            output_biases = Matrix2D(numberof_output_nodes, 1);
            output_biases.randomizeMatrix();
        }
        Matrix2D feedForward(Matrix2D input){

        }

};

Answer 1

问题是当您为 class 定义其他构造函数（默认构造函数除外）时，编译器不会自动生成默认构造函数。

要解决提到的错误，只需添加下面显示的构造函数之一：

 Matrix2D() = default;

或

Matrix2D()
{
    std::cout<<"default constructor"<<std::endl;
}

进入您的 Matrix2D class 定义。以上两个都可以。

错误2

您的 feedForward 函数没有 return 任何东西。您应该在其正文中添加一个 return 语句。

Matrix2D feedForward(Matrix2D input)
{
     return Matrix2D(); //added this return
}

Using a classes object with constructor in another class. error : no matching function for call

Using a classes object with constructor in another class. error : no matching function for call

c++

constructor

class