Throw Bad_alloc exception if not enough memory - c++

Question

I just need to be sure I have enough memory available to the bi-dimensional array map. So I think I'd have to put a try catch bad:alloc in every row of map or perhaps with no throw would be more elegant. But I can't get with it. Any help would be appreciated...
I've read some articles about writing something like:
map[i] = new int [columns];
if (map[i] == NULL)
cout << “No enough memory”;
I don't like this solution and I've read that is not very reliable one.
fillmaze is a function called inside the constructor of maze..
void Maze::setupMaze(int r, int c, int l){
rows = r;
columns = c;
level = l;
fillMaze();
addBorders();
centerWalls();
getaway();
addWalls();
}
void Maze::fillMaze(){
map = new int* [rows];
for (int i = 0; i < rows; i++) {
map[i] = new int[columns];
}
//Inicializamos toda la tabla
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
map[i][j] = PASSAGE;
}
}
}
Also delete [] map is not enough right ? I'm doing in the destructor of the class:
Maze::~Maze(void)
{
for (int i = 0; i < rows; ++i)
delete[] map[i];
delete[] map;
}

Answer 1

This is why you should use std::vector<> as it will handle all the memory management for you correctly.
Issue 1: new never returns NULL (for pedants the normal new as used below). Also note in C++ we use nullptr not NULL for type safety.
map[i] = new int [columns];
if (map[i] == NULL) // This will never be NULL
cout << “No enough memory”; // So this will never print anything.
If fillmaze() is called from the constructor. Then if it throws an exception your destructor is never called. This means you have to deal with any allocation failure in place.
map = new int* [rows]; // could throw.
for (int i = 0; i < rows; i++) {
map[i] = new int[columns]; // could throw
}
So you have to handle and be able to detect what has been allocated and thus what needs to be dallocated.
try
{
map = nullptr; // Init to nullptr to make sure
// you can distinguish between valid state
// and what could have randomly been in memory.
map = new int* [rows]{nullptr}; // Initialize all elements to nullptr.
// If any throw you don't want your code
// to start releasing random pointers.
// calling delete on nullptr is fine.
for (int i = 0; i < rows; i++) {
map[i] = new int[columns]{PASSAGE};
}
}
catch(...) // catch all exceptions.
{
if (map != nullptr) { // You should only loop over
// map if it has been allocated.
for (int i = 0; i < rows; i++) {
delete [] map[i];
}
}
delete [] map; // delete the map.
throw; // rethrow exception
}
Your destructor is dine.
But you can simplify this by simply using a vector:
std::vector<std::vector<int>> maze{std::vector<int>{PASSAGE, columns}, rows};