[英]C++ Properly deallocate multidimensional array with underlying contiguous memory
我有一個為3d數組分配內存的函數。 目的是確保內存是連續的,但也具有a[k][j][i]
語法的便利性:
double *** allocate_3d(const int& sz, const int& sy, const int& sx){
double * aMem = new double[sz*sy*sx];
double *** array = new double**[sz];
for(int k=0; k<sz; k++){
array[k] = new double*[sy];
for(int j=0; j<sy; j++){
array[k][j]= aMem + k*sy*sx + j*sx;
}
}
return array;
}
假設我這樣調用函數
x = allocate_3d(wdz,wdy,wdx);
我該如何正確地釋放x? 我嘗試了以下方法:
void delete_3d(double *** array, const int& sz, const int& sy, const int& sx){
for(int k=0; k<sz; k++){
for(int j=0; j<sy; j++){
delete[] array[k][j];
}
delete[] array[k];
}
delete[] array;
}
但是運行Valgrind會產生錯誤,並且似乎表明內存未正確釋放。
實際上應該是這樣的:
void delete_3d(double *** array, const int& sz, const int& sy, const int& sx) {
// first, restore the pointer to the actual aMem
double * aMem = array[0][0];
// only one dimension was allocated in the loop,
// so only one loop should be deallocating things
for(int k = 0; k < sz; k++) {
delete [] array[k];
}
delete[] array;
delete[] aMem;
}
包裝std::vector
可以同時獲得:連續的內存和合理簡單的訪問語法,並且沒有額外的數組,這對內存,性能和維護都更好:
class Array3d {
public:
Array3d(size_t sx, size_t sy, size_t sz)
: m_sx(sx), m_sy(sy) {
m_array.resize(sx * sy * sz);
}
// Can't overload operator[] with more that one parameter
// so we'll have to do with operator()
double &operator()(size_t x, size_t y, size_t z) {
size_t index = x * m_sx * m_sy + y * m_sy + z;
return m_array[index];
}
private:
size_t m_sx, m_sy;
std::vector<double> m_array;
};
用法示例:
Array3d array(3, 3, 3);
array(0, 1, 2) = 3.14;
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