c++ - 操作符不匹配* =

Question

我一直在学校的一个项目中工作，该项目给了我一些编译问题，想知道我是否可以再看看我做错的事情，我一直遇到的错误在我的测试的第47行中文件说运算符* =不匹配，这让我很困惑。我将包括.h(标题)、. cc(实现)和测试文件。

#ifndef MATRIX_H
#define MATRIX_H
#include <iostream>

using namespace std;
class Matrix {
  public:
  // Construction
   Matrix(int, int, double);
   // Copy construction
   Matrix(const Matrix& m);
   // Destructor
   ~Matrix();
   // Index operators
   const double& operator()(int i, int j) const; //to work on const objects
   double& operator()(int i, int j);
   // Copy assignment operator
   Matrix& operator=(const Matrix& m);
   // Compound arithmetic operators
   Matrix& operator+=(const Matrix& x);
   Matrix& operator-=(const Matrix& x);
   Matrix& operator*=(const Matrix& m);
   Matrix& operator*=(double d); // scalar multiplication
   // Output
   void print(ostream& sout) const; //display the matrix onto output stream
   // sout neatly
   int ncols() const; //return the number of columns
   int nrows() const; // return the number of rows
  private:
   int rows; // number of rows
   int cols; // number of columns
   double **element; //dynamic array to hold data
};
// Arithmetic operators are not members
Matrix operator+(const Matrix& l, const Matrix&r); // return l+r
Matrix operator-(const Matrix& l, const Matrix&r); // return l-r
Matrix operator*(const Matrix& l, const Matrix&r); // return l*r
Matrix operator*(double d, const Matrix& r); // return d*l
Matrix operator*(const Matrix& m, double d); // return l*d
 // Overloaded stream insertion operator
  ostream& operator<<(ostream& out, const Matrix& x);
       #endif

现在这是我的.cc实现文件

#include<iostream>
#include<cstdlib>
#include<stdexcept>
#include<cassert>
#include<iomanip>
#include"Matrix.h"
using namespace std;

Matrix::Matrix(int r=0, int c=0, double d=0.0) // default constructor to initialize everything to zero

{
   rows=r;
   cols=c;
   element=new double*[r];
   for(int i=0;i<r;++i){
     element[i]=new double[c];}
   for(int i=0; i<r; ++i){
      for(int j=0; j<c; ++j){
     element[i][j]=d;
      }
      }
}
Matrix::Matrix(const Matrix& m) 
{

     rows=m.rows;
     cols=m.cols;
     element=new double*[rows];
     for(int i=0;i<rows;++i)
     element[i]= new double[cols];

   for(int i=0; i<rows;++i)
      for(int j=0; j<cols;++j)
     element[i][j]=m.element[i][j];

}



Matrix::~Matrix()
{
   for (int i=0;i<rows;i++){
      delete [] element[i];
   }

   delete [] element;
}



const double& Matrix::operator() (int i, int j) const
{
 return element[i][j];
}




double& Matrix::operator()(int i, int j)
{
   return element[i][j];  
}



Matrix& Matrix::operator=(const Matrix& m)
{

   if(this==&m){
      return *this;
   }
   else if(rows !=m.rows || cols !=m.cols)
   {
      delete [] element;
      rows=m.rows;
      cols=m.cols;
       element= new double*[rows];
       for(int i=0; i<rows;i++){
       element[i]=new double[cols];
     }
      }

   return *this;}




Matrix& Matrix::operator+=(const Matrix& x)
{

     for(int i=0; i<rows; ++i){
     for(int j=0; j<cols; ++j){
     element[i][j]+=x.element[i][j];
     }
  }
   return *this;   
}


Matrix& Matrix::operator-=(const Matrix& x)
{

for(int i=0; i<rows; ++i){
      for(int j=0; j<cols; ++j){
     element[i][j]-=x.element[i][j];
      }
   }
    return *this;

}


 Matrix& Matrix::operator*=(const Matrix& m)
{
      Matrix temp( rows, m.cols);
   for(int i=0; i<temp.rows; ++i){
      for(int j=0; j<temp.cols; ++j){
      for(int k=0; k<cols; ++k){
         temp.element[i][j]+=(element[i][k]* m.element[k][j]);
                 }
     }
      }

      return(*this=temp);


}

Matrix& Matrix::operator*=(double d)
{

for(int i=0; i<rows; ++i){
      for(int j=0; j<cols; ++j){
     element[i][j] *= d;
      }
}
return *this;
}


void Matrix::print(ostream& sout) const
{


 for (int i = 0; i < rows; ++i) {
   sout << element[i][0];
    for (int j = 1; j < cols; ++j) {
     sout << " " << element[i][j];
       }
    sout << endl;
     }

}
int Matrix::ncols() const
{
   return cols;
}


int Matrix::nrows() const
{
   return rows;
}

Matrix operator+(const Matrix& l, const Matrix&r)
{
   Matrix temp(l);
   return(temp+=r);

}

Matrix operator-(const Matrix& l, const Matrix&r)
{
    Matrix temp(l);
    return (temp -=r);
}

Matrix operator*(const Matrix& l, const Matrix&r)
{
   Matrix temp(l);
   return (temp*=r);
}

Matrix operator*(double d, const Matrix&r)
{
   return(r*d);
}

Matrix operator*(const Matrix& m, double d)
{
    Matrix temp(m);
    return(temp*=d); 
}

ostream& operator<<(ostream& out, const Matrix& x)
{
   x.print(out);
    return out;
}

现在这是我的测试文件，我尝试在其中编译时出现错误:

test_matrix.cc:47:13:错误:“operator * =”不匹配(操作数类型为“std::ostream {aka std::basic_ostream}”和“int”)
cout <

#include<iostream>
#include"Matrix.h"
#include"Matrix.cc"
 using namespace std;

int main()
{

   Matrix m1(3,3,2.0);
   Matrix m2(3,3,3.0);

   cout<<"****Testing readMatrixData, and overoladed <<"<<endl;
   cout<<"Matrix m1 is:"<<endl;
   cout<<m1;

   cout<<"Matrix m2 is:"<<endl;
   cout<<m2;

   cout<<"****Testing index subscript operator"<<endl;
   cout<<"m1(2,1) is "<<m1(2,1)<<endl;
   cout<<"Now Set m1(2,1) to -19"<<endl;
   m1(2,1)=-19;
   cout<<"m1 has "<<m1.nrows()<<"rows."<<endl;
   cout<<"m1 has "<<m1.ncols()<<"columns."<<endl;
   cout<<"m1 is now:"<<endl;
   cout<<m1;

   Matrix m3=m1+m2;
   cout<<"Matrix m3 = m1 + m2:"<<endl;
   cout<<m3;

   Matrix m4=m1-m2;
   cout<<"Matrix m4 = m1 - m2:"<<endl;
   cout<<m4;

   Matrix m5=m3*m4;
   cout<<"Matrix m5 = m3 * m4:"<<endl;
   cout<<m5;

   Matrix m6=m3;
   cout<<"After m6 =m3 matrix m6 is:"<<endl;
   cout<<m6;


   cout<<"****Testing scalar multiplication"<<endl;
   cout<<"m3 *= 2 and m3 is now:"<<endl;
   cout<<m3 *= 2.0;

   Matrix m7 = m3 * 2.0;
   cout<<"****Testing matrix times a constant"<<endl;
   cout<<"m7 = m3 * 2 and m7 is:"<<endl;
   cout<<m7;

   Matrix m8 = 2.0 * m3;
   cout<<"****Testing a scalar times a matrix"<<endl;
   cout<<"m8 = 2 * m3 and m8 is:"<<endl;
      cout<<m8;

        Matrix  m9(2,2,2.0);
      cout<<"Matrix m9 is"<<endl;
   cout<<m9;

         Matrix m10(2,2,1.0);
    cout<<"Matrix m10 is"<<endl;
    cout<<m10;

    cout<<"Testing *= with m9 *= m10. m9 is:"<<endl;
   m9= m9*=m10;
   cout<<m9;

    cout<<"Testing += with m9 += m10. m9 is:"<<endl;
   m9=m9+=m10;

    cout<<"Testing -= with m9 -= m10. m9 is:"<<endl;
   m9=m9-=m10;


    return 0;
 }

Answer 1

error: no match for ‘operator*=’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘int’)

运算符 *=的 precedence低于运算符 <<，因此， cout << m3 *= 2.0被评估为 (cout << m3) *= 2.0，这会产生错误。

您需要使用括号来获得所需的求值顺序。例如。:

cout << (m3 *= 2.0);