为什么我们可以删除数组,但不知道C/C++中的长度?

malloc new

int *a = new int[N];
std::cout << sizeof(a);

sizeof(int *)

std::vector

std::vector size

malloc

AllocSize()

new[]

size_t

std::vector

/* holds an array of @a TValue objects which are created at construction and destroyed at destruction. interface borrows bits from std::vector */
template<typename TValue>
class t_array {
    t_array(const t_array&); // prohibited
    t_array operator=(const t_array&); // prohibited
    typedef t_array<TValue>This;
public:
    typedef TValue value_type;
    typedef value_type* pointer;
    typedef const value_type* const_pointer;
    typedef value_type* const pointer_const;
    typedef const value_type* const const_pointer_const;
    typedef value_type& reference;
    typedef const value_type& const_reference;

    /** creates @a count objects, using the default ctor */
    t_array(const size_t& count) : d_objects(new value_type[count]), d_count(count) {
        assert(this->d_objects);
        assert(this->d_count);
    }

    /** this owns @a objects */
    t_array(pointer_const objects, const size_t& count) : d_objects(objects), d_count(count) {
        assert(this->d_objects);
        assert(this->d_count);
    }

    ~ t_array() {
        delete[] this->d_objects;
    }

    const size_t& size() const {
        return this->d_count;
    }

    bool empty() const {
        return 0 == this->size();
    }

    /* element access */
    reference at(const size_t& idx) {
        assert(idx < this->size());
        return this->d_objects[idx];
    }

    const_reference at(const size_t& idx) const {
        assert(idx < this->size());
        return this->d_objects[idx];
    }

    reference operator[](const size_t& idx) {
        assert(idx < this->size());
        return this->d_objects[idx];
    }

    const_reference operator[](const size_t& idx) const {
        assert(idx < this->size());
        return this->d_objects[idx];
    }

    pointer data() {
        return this->d_objects;
    }

    const_pointer data() const {
        return this->d_objects;
    }

private:
    pointer_const d_objects;
    const size_t d_count;
};

• t_array