5 methods for c++ shared_ptr point to an array

c++ shared_ptr point to an array

Guide

shared_ptr

Prior to C++17, shared_ptr could not be used to manage dynamically allocated arrays. By default, shared_ptr will call delete on the managed object when no more references remain to it. However, when you allocate using new[] you need to call delete[], and not delete, to free the resource.

In order to correctly use shared_ptr with an array, you must supply a custom deleter.

code example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
//OK, pointer to int 999
std::shared_ptr<int> sp(new int(999));


template< typename T >
struct array_deleter
{
void operator ()( T const * p)
{
delete[] p;
}
};

// pointer to int array,
// (1) provide array deleter
std::shared_ptr<int> sp(new int[10], array_deleter<int>());

// (2) or lambda expression
std::shared_ptr<int> sp(new int[10], [](int *p) { delete[] p; });

// (3) or use default_delete
std::shared_ptr<int> sp(new int[10], std::default_delete<int[]>());

// (4) or we can use unique_ptr
std::unique_ptr<int[]> up(new int[10]); // this will correctly call delete[]

// (5) or we use vector<int>, no need to provide deleter
typedef std::vector<int> int_array_t;
std::shared_ptr<int_array_t> sp(new int_array_t(10));

std::memcpy(sp.get()->data(), arr, size);

std::unique_ptr<int[]> has built-in support for arrays to properly delete[] .

image buffer

1
2
3
std::shared_ptr<uchar> pImage(new uchar[length], std::default_delete<uchar[]>());
memcpy(pImage.get(), (void*)(data.sync_image().data().c_str()), length);
cv::Mat image = cv::Mat(height, width, CV_8UC3, pImage.get());

Reference

History

  • 20191012: created.
坚持技术分享,您的支持将鼓励我继续创作!