STL 的 auto_ptr 已經(jīng)棄用, 為了解決手動(dòng)釋放指針內(nèi)存的問(wèn)題, 自定義一個(gè)好使的 AutoPtr 包裝類(lèi), 不足的一點(diǎn)是所有被包裝的類(lèi)必須繼承自 BaseType, 因?yàn)?BaseType 中有當(dāng)前被包裝類(lèi)的對(duì)象的引用計(jì)數(shù)。

每有一個(gè) AutoPtr 對(duì)象的 mPtr 指針指向被包裝類(lèi)的對(duì)象, 那么該被包裝類(lèi)的對(duì)象的引用計(jì)數(shù)就 + 1；每有一個(gè) AutoPtr 對(duì)象析構(gòu), 那么 AutoPtr 對(duì)象的 mPtr 指針指向被包裝類(lèi)的對(duì)象的引用計(jì)數(shù)就 -1, 當(dāng)執(zhí)行AutoPtr 對(duì)象的析構(gòu)函數(shù)發(fā)現(xiàn) mPtr 指針指向的被包裝類(lèi)的對(duì)象的引用計(jì)數(shù)變?yōu)?0 時(shí), 就 delete 掉 mPtr 指針, 釋放被包裝類(lèi)的對(duì)象的內(nèi)存, 從而解決了手動(dòng) delete 釋放內(nèi)存的問(wèn)題。

代碼如下 :

#include <iostream>
#include <vector>
#include <thread>
#include <mutex>

using namespace std;

//自己編寫(xiě)智能指針代理類(lèi) AutoPtr
//mTotalAutoPtrCount 目前只能針對(duì)一種 Tp 類(lèi)型
static int mTotalAutoPtrCount = 0; //使用 mCurCount 判斷當(dāng)前是 auto_p1 還是 auto_p2

template<typename Type>
class AutoPtr;

class BaseType{
public:
    //AutoPtr * autoPtr;
    int curRefCount = 0; //當(dāng)前對(duì)象的 AutoPtr 引用計(jì)數(shù)

    BaseType(){

    }
};

//如何讓 Type 繼承自 BaseType ?

template<typename Type>
class AutoPtr {
private:
    //外部的數(shù)據(jù)
    BaseType* mPtr = nullptr;
    int curCount = 0;

public:
    explicit AutoPtr() throw() {
        processCurCount("AutoPtr() Constructor");
    }

    explicit AutoPtr(BaseType *_p) throw(): mPtr(_p) {
        ((*_p).curRefCount) ++; //AutoPtr 對(duì)象引用 BaseType 對(duì)象
        processCurCount("AutoPtr(BaseType *_p) Constructor");
    }

    //拷貝構(gòu)造函數(shù)        //注意 : 這么寫(xiě)不好使, 必須是 const AutoPtr<Type>& autoPtr 拷貝構(gòu)造函數(shù)才會(huì)執(zhí)行 !
//    AutoPtr(const AutoPtr<BaseType>& autoPtr): mPtr(autoPtr.mPtr){
//        cout << "*************** Auto CopyConstructor *******************" << endl;
//        (autoPtr.value() -> curRefCount) ++;
//        processCurCount("AutoPtr CopyConstructor");
//    }

    //拷貝構(gòu)造函數(shù)
    AutoPtr(const AutoPtr<Type>& autoPtr): mPtr(autoPtr.mPtr){
        cout << "*************** Auto CopyConstructor *******************" << endl;
        (autoPtr.value() -> curRefCount) ++;
        processCurCount("AutoPtr CopyConstructor");
    }

//    ~AutoPtr() {
//        count--;
//       if(count < 1){
//           delete _M_ptr;
//       }
//    }

    ~AutoPtr() {
        cout << "-------------- ~AutoPtr() Pre ----------"<< endl;
        mTotalAutoPtrCount --;
        cout << "AutoPtr deConstructor, auto_p" << curCount
                << " mTotalAutoPtrCount = " << mTotalAutoPtrCount << endl << endl;
        processMPtr("AutoPtr deConstructor");
        cout << "-------------- ~AutoPtr() Back ----------"<< endl;
    }

    //如果要進(jìn)行 * 號(hào)操作, 那么直接返回里面的 _M_ptr
    BaseType* operator*() {
        return mPtr;
    }

    AutoPtr* operator=(AutoPtr& tp) {
        cout << "operator=(AutoPtr& tp)" << endl;
        (tp.mPtr) -> curRefCount ++;
        processMPtr("AutoPtr operator=(AutoPtr& tp)");
        mPtr = tp.mPtr;
        return this;
    }

    AutoPtr* operator=(BaseType& tp) {
        cout << "operator=(BaseType& tp)" << endl;
        tp.curRefCount ++;
        processMPtr("AutoPtr operator=(BaseType& tp)");
        mPtr = &tp;
        return this;
    }

    Type * value() const {
        if(mPtr == nullptr){
            return nullptr;
        }
        return reinterpret_cast<Type*>(mPtr);; //(Type*)(mPtr);
    }

private:
    void processCurCount(const string& preFix){
        printf("processCurCount Pre, preFix = %s, mTotalAutoPtrCount = %d \n", preFix.c_str(), mTotalAutoPtrCount);
        mTotalAutoPtrCount ++;
        for(int i = 0; i < 10; ++i){
            if(mTotalAutoPtrCount == i){
                curCount = mTotalAutoPtrCount;
            }
        }
        printf("processCurCount Back, preFix = %s, auto_p%d \n", preFix.c_str(), curCount);
    }

    void processMPtr(const string& preFix){
        printf("processMPtr(const string& preFix) mPtr = %x \n", mPtr);
        if(mPtr != nullptr){
            (*mPtr).curRefCount --;
            printf("processMPtr(const string& preFix)  (*mPtr).curRefCount = %d \n", (*mPtr).curRefCount);

            if((*mPtr).curRefCount == 0){ //不用 < 1, 防止多線程出毛病
                printf("%s auto_p%d.curRefCount <= 1, delete auto_p%d mPtr= %x \n", preFix.c_str(), curCount, curCount, mPtr);
                delete mPtr;
                mPtr = nullptr;
            }
        }
    }
};

class Test : public BaseType{
public:

    //Test* test;           //為了讓 AutoPtr 來(lái)管理指針, 就不要使用 Test* 了
    AutoPtr<Test>* mTest;   //測(cè)試循環(huán)引用

    //類(lèi)的非靜態(tài)成員變量, 在類(lèi)的實(shí)例化過(guò)程中(構(gòu)造對(duì)象)才在棧區(qū)或者堆區(qū)為其分配內(nèi)存
    //因?yàn)?AutoPtr<Test> 中存儲(chǔ)的 Test* 指向的對(duì)象必定是在堆區(qū)中創(chuàng)建的, 所以 Test 類(lèi)中的 mTestRef 即使不使用指針也不會(huì)在棧區(qū)里創(chuàng)建
    //頂多調(diào)用一次 AutoPtr 的拷貝構(gòu)造函數(shù)
    //AutoPtr<Test> mTestRef;

    string content;

    Test() {
        cout << "Test Constructor" << endl;
    }

    Test(string content) : content(content) {
        cout << "Test Constructor, content = " << content << endl;
    }

    Test(Test &t) {
        cout << "Test CopyConstructor" << endl;
    }

    ~Test() {
        cout << "Test DeConstructor, this addr = " << this << endl;
    }
};

//測(cè)試一次賦值
void test_auto_ptr1_simple_assign(){
    AutoPtr<Test> auto_p1(new Test("Test1"));
    AutoPtr<Test> auto_p2(new Test("Test2"));
    auto_p1 = auto_p2;

    cout << "auto_p1 content = " << auto_p1.value()->content << endl;
}

/**
    Test Constructor
    AutoPtr Constructor(), auto_p1
    Test Constructor
    AutoPtr Constructor(), auto_p2
    AutoPtr operator=(AutoPtr& tp)  auto_p1.curRefCount <= 1, delete auto_p1 mPtr=0xe65eb0
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1
    AutoPtr deConstructor, auto_p1 mTotalAutoPtrCount = 0
    AutoPtr deConstructor auto_p1.curRefCount <= 1, delete auto_p1 mPtr=0xe65ed0

    Process finished with exit code 0
 */

//測(cè)試多次賦值
void test_auto_ptr2_multi_assign(){
    AutoPtr<Test> auto_p1(new Test());
    AutoPtr<Test> auto_p2(new Test());
    AutoPtr<Test> auto_p3(new Test());
    auto_p1 = auto_p2;
    auto_p3 = auto_p2;
    auto_p1 = auto_p3;
}

/**
    Test Constructor
    AutoPtr Constructor(), auto_p1
    Test Constructor
    AutoPtr Constructor(), auto_p2
    Test Constructor
    AutoPtr Constructor(), auto_p3
    AutoPtr operator=(AutoPtr& tp)  auto_p1.curRefCount <= 1, delete auto_p1 mPtr=0x1015eb0
    AutoPtr operator=(AutoPtr& tp)  auto_p3.curRefCount <= 1, delete auto_p3 mPtr=0x1015ef0
    AutoPtr deConstructor, auto_p3 mTotalAutoPtrCount = 2
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1
    AutoPtr deConstructor, auto_p1 mTotalAutoPtrCount = 0
    AutoPtr deConstructor auto_p1.curRefCount <= 1, delete auto_p1 mPtr=0x1015ed0

    Process finished with exit code 0
 */

//測(cè)試循環(huán)引用 (沒(méi)毛病)
void test_auto_ptr3_cycle_assign(){
    AutoPtr<Test> auto_p1(new Test("Test1"));
    AutoPtr<Test> auto_p2(new Test("Test2"));
    auto_p1.value() -> mTest = &auto_p2;
    auto_p2.value() -> mTest = &auto_p1;
    cout << "auto_p1 content = " << auto_p1.value()->content << endl;
    cout << "auto_p2 content = " << auto_p2.value()->content << endl;
}

/**
    AutoPtr() Constructor auto_p1
    AutoPtr(BaseType *_p) Constructor auto_p2
    AutoPtr() Constructor auto_p3
    AutoPtr(BaseType *_p) Constructor auto_p4
    auto_p1 content = Test1
    auto_p2 content = Test2
    AutoPtr deConstructor, auto_p4 mTotalAutoPtrCount = 3
    AutoPtr deConstructor auto_p4.curRefCount <= 1, delete auto_p4 mPtr=0x1025f00
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 2
    AutoPtr deConstructor auto_p2.curRefCount <= 1, delete auto_p2 mPtr=0x1025eb0
    
    Process finished with exit code 0
 */

//測(cè)試返回值, AutoPtr 對(duì)象從函數(shù)返回后, 函數(shù)的作用域消失, 函數(shù)內(nèi)部的 AutoPtr 對(duì)象析構(gòu)會(huì)影響返回的 AutoPtr 對(duì)象嗎? 不會(huì)
AutoPtr<Test> return_auto_ptr(){
    AutoPtr<Test> auto_p1(new Test("Test1"));
    AutoPtr<Test> auto_p2;
    cout << "auto_p2 = auto_p1 Pre" << endl;
    auto_p2 = auto_p1;
    cout << "auto_p2 = auto_p1 End" << endl;
    return auto_p2;
}

void test_auto_ptr4_return(){
    AutoPtr<Test> autoPtr = return_auto_ptr(); //這里執(zhí)行拷貝構(gòu)造函數(shù)
    cout << "test_auto_ptr4_return(), autoPtr content = " << autoPtr.value()->content << endl;
}

/**
    AutoPtr() Constructor auto_p1
    AutoPtr(BaseType *_p) Constructor auto_p2
    AutoPtr() Constructor auto_p3
    auto_p2 = auto_p1 Pre
    auto_p2 = auto_p1 End
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 2
    test_auto_ptr4_return(), autoPtr content = Test1
    AutoPtr deConstructor, auto_p3 mTotalAutoPtrCount = 1
    AutoPtr deConstructor auto_p3.curRefCount <= 1, delete auto_p3 mPtr=0xfd5eb0

    Process finished with exit code 0
*/


//測(cè)試初始化 (好使)
void test_auto_ptr_init(){
    AutoPtr<Test> tempPtr = AutoPtr<Test>(new Test("test_auto_ptr_init"));
    cout << "tempPtr2 = tempPtr Pre, tempPtr value refCount = " << tempPtr.value()->curRefCount << endl;
    AutoPtr<Test> tempPtr2 = tempPtr;
    //這里不會(huì)執(zhí)行 operator = 函數(shù), 但是會(huì)執(zhí)行拷貝構(gòu)造函數(shù)
    cout << "tempPtr2 = tempPtr Back, tempPtr value refCount = " << tempPtr.value()->curRefCount << endl;
}

/**
    Test Constructor, content = test_auto_ptr_init
    processCurCount Pre, preFix = AutoPtr(BaseType *_p) Constructor, mTotalAutoPtrCount = 0
    processCurCount Back, preFix = AutoPtr(BaseType *_p) Constructor, auto_p1
    tempPtr2 = tempPtr Pre, tempPtr value refCount = 1
    *************** Auto CopyConstructor *******************
    processCurCount Pre, preFix = AutoPtr CopyConstructor, mTotalAutoPtrCount = 1
    processCurCount Back, preFix = AutoPtr CopyConstructor, auto_p2
    tempPtr2 = tempPtr Back, tempPtr value refCount = 2
    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1

    processMPtr(const string& preFix) mPtr = 6a5ed0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 1
    -------------- ~AutoPtr() Back ----------
    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p1 mTotalAutoPtrCount = 0

    processMPtr(const string& preFix) mPtr = 6a5ed0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 0
    AutoPtr deConstructor auto_p1.curRefCount <= 1, delete auto_p1 mPtr= 6a5ed0
    -------------- ~AutoPtr() Back ----------
    請(qǐng)按任意鍵繼續(xù). . .

    Process finished with exit code 0
 */

//測(cè)試多線程
AutoPtr<Test> globalPtr = AutoPtr<Test>(new Test("thread AutoPtr"));
mutex mut;

void thread_func(int num) {
    //加鎖解決當(dāng)前同步寫(xiě)的問(wèn)題
    mut.lock();

    std::cout << "------ thread_func Pre ------" << endl;

    std::cout << "thread_func num = " << num << endl; //cout 不是線程安全的

    AutoPtr<Test> innerPtr = globalPtr; //內(nèi)部有風(fēng)險(xiǎn)，取數(shù)據(jù)無(wú)所謂，如果是寫(xiě)數(shù)據(jù)

    std::cout << "globalPtr content = " << globalPtr.value() -> content << std::endl;

    std::cout << "------ thread_func Back ------" << endl;

    mut.unlock();
}

//測(cè)試多線程 (好使)
void test_auto_ptr5_multi_thread(){
    std::thread t1(thread_func, 1);
    std::thread t2(thread_func, 2);
    std::thread t3(thread_func, 3);
    std::thread t4(thread_func, 4);
    std::thread t5(thread_func, 5);
    t1.join();
    t2.join(); //如果只有 t1.join(), 那么 exit code 就是 3 而不是 0
    t3.join();
    t4.join();
    t5.join();
}

/**
    Test Constructor, content = thread AutoPtr
    processCurCount Pre, preFix = AutoPtr(BaseType *_p) Constructor, mTotalAutoPtrCount = 0
    processCurCount Back, preFix = AutoPtr(BaseType *_p) Constructor, auto_p1
    ------ thread_func Pre ------
    thread_func num = 1
    *************** Auto CopyConstructor *******************
    processCurCount Pre, preFix = AutoPtr CopyConstructor, mTotalAutoPtrCount = 1
    processCurCount Back, preFix = AutoPtr CopyConstructor, auto_p2
    globalPtr content = thread AutoPtr
    ------ thread_func Back ------
    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1

    processMPtr(const string& preFix) mPtr = fb5eb0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 1
    -------------- ~AutoPtr() Back ----------
    ------ thread_func Pre ------
    thread_func num = 2
    *************** Auto CopyConstructor *******************
    processCurCount Pre, preFix = AutoPtr CopyConstructor, mTotalAutoPtrCount = 1
    processCurCount Back, preFix = AutoPtr CopyConstructor, auto_p2
    globalPtr content = thread AutoPtr
    ------ thread_func Back ------
    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1------ thread_func Pre ------
    thread_func num = 3


    processMPtr(const string& preFix) mPtr = fb5eb0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 1
    -------------- ~AutoPtr() Back ----------
    *************** Auto CopyConstructor *******************
    processCurCount Pre, preFix = AutoPtr CopyConstructor, mTotalAutoPtrCount = 1
    processCurCount Back, preFix = AutoPtr CopyConstructor, auto_p2
    globalPtr content = thread AutoPtr
    ------ thread_func Back ------
    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p2 mTotalAutoPtrCount = 1

    processMPtr(const string& preFix) mPtr = fb5eb0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 1
    -------------- ~AutoPtr() Back ----------
    請(qǐng)按任意鍵繼續(xù). . .

    -------------- ~AutoPtr() Pre ----------
    AutoPtr deConstructor, auto_p1 mTotalAutoPtrCount = 0

    processMPtr(const string& preFix) mPtr = fb5eb0
    processMPtr(const string& preFix)  (*mPtr).curRefCount = 0
    AutoPtr deConstructor auto_p1.curRefCount <= 1, delete auto_p1 mPtr= fb5eb0
    -------------- ~AutoPtr() Back ----------

    Process finished with exit code 0
*/

int main() {
//    test_auto_ptr1_simple_assign();
//    test_auto_ptr2_multi_assign();
//    test_auto_ptr3_cycle_assign();
//    test_auto_ptr4_return();
    test_auto_ptr5_multi_thread();

//    test_auto_ptr_init();

    system("pause");
    return 0;
}