从函数返回指向二维数组的指针

Question

In order to understand how pointer work I wrote this function which has to return a 3*3 matrix.

int** Matrix::getMatrix(){
    cout<<"The  matrix is: \n";
    int (*p)[3]=m;

    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
        cout<<m[i][j]<<"\t";
        }
        cout<<"\n";
    }
    return p;

}  

Here m is a 3*3 array.But at the line return p; it gives the error return value type does not match function type .

With p am I not returning a pointer to a 3*3 matrix.?What's wrong with this.Can someone please help me to correct this.

Answer 1

int (*)[3] and int** are not the same type:

• int** is a pointer to a pointer to int
• int (*)[3] is a pointer of an array of 3 int .

Even if int [3] may decay to int* , pointer on there different type are also different.

The correct syntax to return int (*)[3] would be:

int (*Matrix::getMatrix())[3];

or with typedef :

using int3 = int[3];

int3* Matrix::getMatrix();

And as m is int[3][3] , you may even return reference ( int(&)[3][3] ):

int (&Matrix::getMatrix())[3][3];

and with typedef:

using mat3 = int[3][3];
mat3& Matrix::getMatrix();

It would be more intuitive with std::array or std::vector