c++ - Deallocating Dynamic 2D Array with Template -

c++ - Deallocating Dynamic 2D Array with Template -

i having error in c++ application having problem debugging. have looked online, , appear doing of allocation/deallocation right way. here code:

template <typename t> class matrix { private: int _rows; int _cols; t** _matrix; public: matrix(int r, int c); ~matrix(); t getvalue(int r, int c); }; template <typename t> matrix<t>::matrix(int r, int c) { _rows = r; _cols = c; _matrix = new t*[_rows]; for(int = 0; < _rows; i++) _matrix[i] = new t[_cols]; for(int = 0; < _rows; i++) for(int j = 0; j < _cols; j++) _matrix[i][j] = null; } template <typename t> matrix<t>::~matrix() { for(int = 0; < _rows; i++) delete [] _matrix[i]; delete [] _matrix; } template <typename t> t matrix<t>::getvalue(int r, int c) { if(r < 0 || r >= _rows || c < 0 || c > _cols) { throw -1; homecoming null; } homecoming _matrix[r][c]; }

and client code...

int main() { matrix<int> mymatrix(3, 3); mymatrix.getvalue(1, 1); // mymatrix.~matrix(); // don't anymore }

as variable "mymatrix" goes out of scope, error:

unhandled exception @ 0x103159da (msvcr1000d.dll)...access violation reading location 0xfeeefee2. , brought file "dbgdel.cpp" _asserte(_block_type_is_valid(phead->nblockuse));

please help!

edit:

okay, neglected give information. please see below:

i have additional method called "t dot(matrix)" i've got 2 methods called "columns()" , "rows()" getters _cols , _rows. , method called "setvalue(int r, int c, t value)" sets _matrix[r][c] = value. don't think showing implementation necessary these.

template <typename t> t matrix<t>::dot(matrix<t> m) { if(_cols > 1 || m.columns() > 1 || _rows != m.rows()) { throw -1; homecoming null; } t value = 0; for(int = 0; < _rows; i++) { value += _matrix[i][0] * m.getvalue(i, 0); } homecoming value; // whoops, here, forgot type }

and client...

int main() { matrix<int> intm1(3, 1); matrix<int> intm2(3, 1); intm1.setvalue(0, 0, 1); intm1.setvalue(1, 0, 1); intm1.setvalue(2, 0, 1); intm2.setvalue(0, 0, 1); intm2.setvalue(1, 0, 1); intm2.setvalue(2, 0, 1); std::cout << intm1.dot(intm2) << endl; }

this generates same error above, when "dot()" function called.

with edit, issue here still lack of re-create constructor , assignment operator (see reply lastly question). problem when pass matrix value function, re-create constructor invoked create copy, since haven't defined 1 c++ utilize default re-create constructor, makes shallow copy. consequently, you'll end getting new matrix shares pointer same elements old matrix. when new matrix goes out of scope, destructor fire, cleaning array used other matrix. when original matrix goes out of scope , cleaned up, seek delete already-deleted array, causing crash.

to prepare this, need implement re-create constructor , assignment operator correctly duplicate resources. there's rule-of-thumb called rule of 3 says if have destructor, need re-create constructor , assignment operator prevent these sorts of bugs. seek implementing these missing functions , see if problem clears up.

c++ arrays memory-management dynamic