运算符+类的C ++重载

Question

This is for assignment in my faculty, I want to do overload for operator + to matrix I create new matrix an put the sum in this matrix and I print it but it print nothing so can anyone help me to solve this problem?

class matrix
{
private:
  int* data;
  int row, col;

public:
  matrix();
  matrix(int r, int c, int num[]);
  friend ostream& operator << (ostream& out, matrix mat1);
  friend istream& operator >> (istream& in, matrix& mat);
  int getrow();
  int getcol();
  int getdata(int i);
  int setrow(int r);
  int setcol(int c);
  int setdata(int num[]);
  matrix operator+ (const matrix& mat2);
};

Now I write this code an it prints nothing can anyone help me to solve this? first I make setter and getter for the data.

matrix::matrix(){
  row=0;
  col=0;
}

matrix::matrix(int r, int c, int num[])
{
  row = r;
  col = c;
  data = new int[r*c];
  for(int i=0; i < (r*c); i++)
    data[i] = num[i];
}

matrix::getrow() { return row; }
matrix::getcol() { return col; }

matrix::setrow(int r) { row=r; }
matrix::setcol(int c) { col=c; }

matrix matrix::operator+ (const matrix& mat2)
{
  matrix mat3;
  for(int i=0; i < mat3.getrow() * mat3.getcol(); i++) {
    mat3.data[i] = data[i] + mat2.data[i];
  }
  return mat3;
}

---

int main(){
  int num2 [] = {1,2,3,4,5,6,7,8,8};
  int num3 [] = {1,0,0,0,1,0,0,0,1};

  matrix x;

  matrix mat2(3, 3, num2);
  matrix mat3(3, 3, num3);
  matrix mat4;
  mat4 = mat2 + mat3;
  cou << mat4;

  return 0;
}

Answer 1

You did not set the dimensions of mat3 , so getrow() and getcol() both return 0 , and the buffer is too small to contain the data you put it in, so you also suffer from buffer overflow.

Add a private constructor that only accepts the dimensions without initializing values.

Your next problem is that you don't have a copy/move constructor/operator=(), so the assignment into mat3 in main() is not well defined.

Answer 2

Here are some suggestions

1. Initialization mistake

try to add a constructor overload method like this:

matrix::matrix(int r, int c)
{
    row = r;
    col = c;
    data = new int[r*c];
    for (int i = 0; i < r*c; i++) {
        data[i] = 0;
    }
}

then in operator+ overloading function, initiate mat3 by using this method:

matrix mat3(mat2.getrow(), mat2.getcol());

2.overload = operator is essential since you decide to mat4 =

matrix matrix::operator= (const matrix& from_mat)
{
    matrix to_mat(from_mat.getrow(), from_mat.getcol());
    for (int i = 0; i < from_mat.getrow() * from_mat.getcol(); i++) {
        to_mat.data[i] = from_mat.data[i];
    }
    return to_mat;
}

3. in main function, just use matrix mat4 = mat2 + mat3;

Answer 3

There are many things wrong with your post. Others have pointed a few things out, here is a more complete list IMO:

• You are asking about a display issue, but your title is about operator+ , and you do not provide the implementation of ostream& operator<< ( ostream&, matrix& ) . There is also no reason why displaying the contents of a matrix should modify it, so it should be ostream& operator<< ( ostream&, const matrix& ) (this will also eliminate the need for the pass-by-value variant).
• Some of your constructors allocate memory, but you did not define a destructor ( ~matrix() ) to handle deallocation, and have no copy constructor ( matrix( const matrix& ) ). Read about destructors and memory management.
• You overload the default constructor matrix() but it is currently not possible to update the size or contents of your matrix. What is the point of a default constructor if the empty matrix it creates cannot be changed later on? You should also define data = nullptr in this case.
• The role of the setters for number of rows and columns ( setrow, setcol ) is unclear; setting the size attributes should affect the memory allocation (ie data ), but currently it does not. You also declare those methods as returning int s, but do not return anything. You should delete both of these methods; there is no need for them, and your implementation is currently wrong.
• In operator+ the first thing to check is that the input has the same size as the current matrix. The second thing is to allocate the output correctly (with matrix( row, col ) ), which implies the need for an additional constructor matrix(int r, int c) (as suggested by the other answers). The third is to declare this method as constant matrix operator+ ( const matrix& other ) const .
• There is a typo in your main, cou should be std::cout .
• Finally, what happens if I write matrix x( -1, -5, NULL ); ?