智能指针主要是做了两件事情：
- 申请内存，我们用模板指针 T* ptr
- 另一个进行计数并销毁清理对象
注意多个智能指针里的ptr可能会指向同一快内存，所以计数的变量也是要同步的，在这里我们用一个指针int* count来计数，每次新建一个共享指针就对count进行浅拷贝，这样多个指针指针就能同步进行更新计数了
当我们重载operator=的时候，要注意如果原来的共享指针已经有对象，需要将原来的引用计数减一并判断是否需要释放内存
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| #include<iostream>
#include <memory>
using namespace std;
template<class T>
class S_ptr
{
public:
S_ptr();
S_ptr(T *p);
~S_ptr();
S_ptr(const S_ptr<T> &org);
S_ptr<T>& operator = (const S_ptr<T> &org);
int get_count();
void get();
private:
int *use_count;
T *ptr;
};
template<class T>
S_ptr<T>::S_ptr() : ptr(), use_count(new int (1)) {
cout << "Allocation11" << endl;
};
template<class T>
S_ptr<T>::S_ptr(T *p) : ptr(p) {
use_count = new int(1);
cout << "Allocation22" << endl;
if (use_count == nullptr) {
p = nullptr;
cout << "Allocation Error" << endl;
return;
}
}
template<class T>
S_ptr<T>::~S_ptr() {
if (--*use_count == 0) {
delete ptr;
ptr = nullptr;
delete use_count;
use_count = nullptr;
}
}
template<class T>
S_ptr<T>::S_ptr(const S_ptr<T> &org) {
ptr = org.ptr;
use_count = org.use_count;
(*use_count)++;
}
template<class T>
S_ptr<T>& S_ptr<T>::operator = (const S_ptr &org) {
if (this->ptr) {
if (--this->use_count == 0) {
delete this->ptr;
delete this->count;
}
this->ptr = org.ptr;
this->use_count = org.use_count;
(*use_count)++;
}
return *this;
}
template<class T>
S_ptr<T>::get_count() {
return *use_count;
}
int main() {
S_ptr<string> p1(new string("hello"));
shared_ptr<int> p(new int(2));
cout << p1.get_count() << endl;
S_ptr<string> p2(p1);
cout << p1.get_count() << endl;
{
S_ptr<string> p3(p1);
cout << p1.get_count() << endl;
}
cout << p1.get_count() << endl;
return 0;
}
|
