c++ - 使用智能指针管理动态内存

Question

在《c++ primer》这本书中看到，两种智能指针管理内存：

shared_ptr<int> sp (new int[10],[](int*p){delete[] p;}):

unique_ptr<int[]> up (new int[10]);

为什么使用shared_ptr的时候不需要指明int[]而可以使用int呢？

Answer 1

uniqe_ptr<int> up(new int), it will be deleted when deleted later.
uniqe_ptr<int []> up(new int[10]), it will delete [] when deleted later.

Incorrect matching will result in errors.

When the shared_ptr standard was set, no one thought of adding an array specialization to the shared_ptr template. So the implementation of shared_ptr<int[]> calling delete[] does not exist.

shared_ptr<int> sp(new int[10]), when deleting later, delete will be used instead of delete [], which will cause an error.

You must tell shared_ptr how to delete this array, which is the [](int*p){delete[] p;}) at the end. Without this, an error will occur when deleting.

Why wasn’t shared_ptr added when setting the standard? Because they forgot/lazy/no one wrote a proposal, probably like this.

In fact, the unique_ptr and shared_ptr of arrays are not very common. Just use vector directly. .

Answer 2

@hearts has already said it quite comprehensively, let me add one more thing.

In most cases, just use vector directly. The standard library has been well optimized. But shared_ptr and unique_ptr are not useless, especially when it comes to polymorphism. For details, please see the section on object-oriented programming of C++ Primer. shared_ptr and unique_ptr are also mentioned before. auto_ptr are all intended to replace naked pointers [dangerous] . In actual situations, it should be said that shared_ptr is used less and unique_ptr is more commonly used.

Of course, both vector and *_ptr are all for RAII. This is another interesting topic.

Some simple opinions, please give me some advice.