在一个命令中使用 2 个重载运算符会导致错误

>我在C++中创建了一个带有重载运算符的矩阵类，我重载了运算符，<<(输出，带有 ostream 库(，运算符 + 添加到矩阵中，运算符 = 用于将一个矩阵分配给另一个矩阵。问题是当我使用

cout<<m1+m2<<endl;

我收到错误

E0349: No operator << matches these operands type are: std::ostream << Matrix

但是如果我执行以下操作：

Matrix m = m1 + m2;
cout<<m<<endl;

它工作完美。 这是<<运算符：

ostream& operator<< (ostream &os,const Matrix& m)
{
if (m.isValid())
{
os << '|';
for (int i = 0; i < m.getRows(); i++)
{
for (int j = 0; j < m.getCols(); j++)
{
os << m.getMatrix()[i][j];
if (j < m.getCols() - 1)
{
os << ',';
}
}
os << '|';
}
}
else
{
os << "invalid matrix!";
}
return os;
}

+ 运算符：

Matrix Matrix::operator+ (Matrix &m)
{
Matrix* answer = new Matrix(m); //allocating space
if (valid && m.valid)//if they are both valid
{
if (colNum == m.colNum&&rowNum == m.rowNum) //if are from same size
{
answer->valid = true; //valid set to be true
for (int i = 0; i < rowNum; i++) //going over the matrix
{
for (int j = 0; j < colNum; j++)
{
answer->matrix[i][j] += matrix[i][j]; //adding data
}
}
}
else
{
//clearing data
delete answer;
answer = new Matrix();
}
}
else
{
//clearing data
delete answer;
answer = new Matrix();
}
return *answer;
}

和 = 运算符：

Matrix Matrix::operator= (Matrix &m)
{
int rows = m.rowNum; //putting cols and rows from the data
int cols = m.colNum;
if (m.valid)
{
matrix = new int*[rows]; //defining the matrix - first allocatin space for rows
for (int i = 0; i < rows; i++) //now allocating space for cols
{
matrix[i] = new int[cols];
}
for (int i = 0; i < rows; i++) //now going over the matrix and putting the data in
{
for (int j = 0; j < cols; j++)
{
matrix[i][j] = m.matrix[i][j];
}
}
}
//putting the rows and cols data
rowNum = m.rowNum;
colNum = m.colNum;
valid = m.valid; //setting to the right valid type
return *this;
}

和类变量：

class Matrix
{
private:
bool valid;
int** matrix;
int rowNum;
int colNum;

有一个复制构造函数、字符串构造函数和一个根据算法获取字符串输入并将其转换为矩阵的构造函数。