在 C++ 中删除指针向量的正确方法

Question

Given the next snipped:

vector<cv::Mat> list; // Hold the pointer values (not the pointers)

for (int index = 0; index < item_count; index++)
{
    jobject bitmap = env->GetObjectArrayElement(listBitmaps, index);

    // BitmapUtils::toMat returns a cv::Mat* which has been created with "new cv::Mat()"
    cv::Mat* mat = BitmapUtils::toMat(bitmap);

    list.push_back(*mat); // Store the object value
}

Is next the correct way to delete the vector object pointers?

for (auto entry : sources)
{
    delete & entry;
}

Note that I can't use a vector of pointers such as vector<cv::Mat *> .

Answer 1

When a Vector instance is reaching its end of scope (end of life) then the destructor of all its containing objects are called. So if you have objects in a vector (not pointers to objects) then you don't need to do any explicit call of deletes, not counting the one in that your object's destructor.

In contrast, if you have pointers in a vector, you need to call delete on those pointers, if you want to release their associated objects, making sure they're still pointing to existing objects (ie not deleted already by some other part of code).

Finally, to make sure you don't have memory leaks, it's always a good idea and advised to make a test run of your program with Valgrind.

Answer 2

"Is next the correct way to delete the vector object pointers?" No, it's not.

If sources has type vector<cv::Mat *> you have to delete the pointers with

for (auto entry : sources)
{
    delete entry;
}

The vector vector<cv::Mat> list; has automatic storage duration. It will be automatically destroyed at the end of its block. It will allocate and deallocate the memory for its elements. You are not allowed to delete the vector or its elements.

If you have to delete the pointer returned by cv::Mat* mat = BitmapUtils::toMat(bitmap);you could do it this way:

vector<cv::Mat> list; // Hold the pointer values

for (int index = 0; index < item_count; index++)
{
    jobject bitmap = env->GetObjectArrayElement(listBitmaps, index);

    // BitmapUtils::toMat returns a cv::Mat* which has been created with "new cv::Mat()"
    cv::Mat* mat = BitmapUtils::toMat(bitmap);

    list.push_back(*mat); // Store the object value
    delete mat;
}