Passing arguments to constructor results in an error - c++

Question

I have a constructor which constructs a matrix, represented by a 2D vector, rows and columns number.
Matrix(const vector<vector<T> >* vect, const size_t rows, const size_t cols) :
matrix(&vect), matrixRows(rows), matrixCols(cols){}
I want to find the transpose of a matrix in one of my functions.
Matrix& trans() const
{
vector<vector<T> > trans(matrixCols, vector<T>(matrixRows));
for(unsigned int i = 0; i < matrixRows; i++)
{
for(unsigned int j = 0; j < matrixCols; j++)
{
trans[j][i] = matrix[i][j];
}
}
return Matrix(&trans, matrixCols, matrixRows);
}
The last line results in an error, because passing a vector this way is wrong.
What is the correct way?
Full error:
Multiple markers at this line
- invalid initialization of non-const reference of type 'Matrix<Complex>&' from an rvalue of type
'Matrix<Complex>'
- required from 'Matrix<T>& Matrix<T>::trans() const [with T = int]'
- invalid initialization of non-const reference of type 'Matrix<double>&' from an rvalue of type
'Matrix<double>'
- invalid initialization of non-const reference of type 'Matrix<int>&' from an rvalue of type 'Matrix<int>'
- required from 'Matrix<T>& Matrix<T>::trans() const [with T = Complex]'
- required from 'Matrix<T>& Matrix<T>::trans() const [with T = double]'
constructor error:
Multiple markers at this line
- invalid conversion from 'const std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > >**' to 'std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > >::size_type
{aka long long unsigned int}' [-fpermissive]
- candidate expects 3 arguments, 1 provided
- no matching function for call to 'std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > >::vector(const std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > >
>**)'
- no known conversion for argument 1 from 'std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >' to 'const std::vector<std::vector<double, std::allocator<double> >,
std::allocator<std::vector<double, std::allocator<double> > > >*'
- candidate: Matrix<T>::Matrix(const std::vector<std::vector<T> >*, size_t, size_t) [with T = double; size_t = long long unsigned int]
- no known conversion for argument 1 from 'std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > >' to 'const std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int>
> > >*'
- candidate: Matrix<T>::Matrix(const std::vector<std::vector<T> >*, size_t, size_t) [with T = int; size_t = long long unsigned int]
- no matching function for call to 'std::vector<std::vector<Complex, std::allocator<Complex> >, std::allocator<std::vector<Complex, std::allocator<Complex> > > >::vector(const std::vector<std::vector<Complex, std::allocator<Complex> >,
std::allocator<std::vector<Complex, std::allocator<Complex> > > >**)'
- invalid conversion from 'const std::vector<std::vector<Complex, std::allocator<Complex> >, std::allocator<std::vector<Complex, std::allocator<Complex> > > >**' to 'std::vector<std::vector<Complex, std::allocator<Complex> >,
std::allocator<std::vector<Complex, std::allocator<Complex> > > >::size_type {aka long long unsigned int}' [-fpermissive]
- no matching function for call to 'std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >::vector(const std::vector<std::vector<double, std::allocator<double> >,
std::allocator<std::vector<double, std::allocator<double> > > >**)'
- invalid conversion from 'const std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >**' to 'std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double,
std::allocator<double> > > >::size_type {aka long long unsigned int}' [-fpermissive]
- no known conversion for argument 1 from 'std::vector<std::vector<Complex, std::allocator<Complex> >, std::allocator<std::vector<Complex, std::allocator<Complex> > > >' to 'const std::vector<std::vector<Complex, std::allocator<Complex> >,
std::allocator<std::vector<Complex, std::allocator<Complex> > > >*'
- candidate: Matrix<T>::Matrix(const std::vector<std::vector<T> >*, size_t, size_t) [with T = Complex; size_t = long long unsigned int]

Answer 1

First off, you probably want the Matrix constructor to take the vector by reference instead of address:
Matrix(const vector<vector<T>>& vect, const size_t rows, const size_t cols)
: matrix(vect), matrixRows(rows), matrixCols(cols)
{
}
(Note that this will cause the vector to be copied into matrix. Depending on the size of the vector, this might be fine - it really depends on the performance requirements of your program.)
Secondly, trans() should not return a reference to a Matrix. Since you are returning the value of a local, the variable will be destroyed when execution leaves the function, so the caller would have no way to make use of it.
Combined with the change to the Matrix constructor above, trans() should compile now:
Matrix trans() const
{
vector<vector<T>> trans(matrixCols, vector<T>(matrixRows));
for(unsigned int i = 0; i < matrixRows; i++)
{
for(unsigned int j = 0; j < matrixCols; j++)
{
trans[j][i] = matrix[i][j];
}
}
return Matrix(trans, matrixCols, matrixRows);
}