简单说明一下__declspec( dllexport )的作用

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首先，建两个文件List.h和List.cpp，List.h为接口文件，List.cpp实现其接口功能
，
代码如下：

List.h

struct ListNode
{
    int       m_nValue;
    ListNode* m_pNext;
};

__declspec( dllexport ) ListNode* CreateListNode(int value);
__declspec( dllexport ) void ConnectListNodes(ListNode* pCurrent, ListNode* pNext);
__declspec( dllexport ) void PrintListNode(ListNode* pNode);
__declspec( dllexport ) void PrintList(ListNode* pHead);
__declspec( dllexport ) void DestroyList(ListNode* pHead);
__declspec( dllexport ) void AddToTail(ListNode** pHead, int value);
__declspec( dllexport ) void RemoveNode(ListNode** pHead, int value);

List.cpp

#include<iostream>
#include "include/List.h"

using namespace std;

// 创建链表节点
ListNode* CreateListNode(int value) {
    ListNode* pNode = new ListNode();
    pNode->m_nValue = value;
    pNode->m_pNext = nullptr;

    return pNode;
}

// 连接链表节点
void ConnectListNodes(ListNode* pCurrent, ListNode* pNext) {
    if (pCurrent == nullptr) {
        cout << "error to connect two nodes!";
        exit(1);
    }

    pCurrent->m_pNext = pNext;
}

// 打印链表节点
void PrintListNode(ListNode* pNode) {
    if (pNode == nullptr)
        cout << "The node is nullptr!";
    else
        cout << pNode->m_nValue << endl;
}

// 打印链表
void PrintList(ListNode* pHead) {
    cout << "PrintList start!" << endl;
    ListNode *pNode = pHead;
    if (pNode == nullptr) {
        cout << "The list is null" << endl;
        exit(1);
    }
    while (pNode != nullptr) {
        cout << pNode->m_nValue << endl;
        pNode = pNode->m_pNext;
    }
    cout << "PrintList end!" << endl;
}

// 销毁列表
void DestroyList(ListNode* pHead) {
    ListNode *pNode = pHead;
    while (pNode != nullptr) {
        pHead = pHead->m_pNext;
        delete pNode;
        pNode = pHead;
    }
}

// 向链表的末尾添加一个节点
void AddToTail(ListNode** pHead, int value) {
    ListNode *pNew = new ListNode();
    pNew->m_nValue = value;
    pNew->m_pNext = nullptr;

    if (*pHead == nullptr)
        *pHead = pNew;
    else {
        ListNode *pNode = *pHead;

        while (pNode->m_pNext != nullptr)
            pNode = pNode->m_pNext;

        pNode->m_pNext = pNew;
    }
}

// 删除列表中值为value的节点
void RemoveNode(ListNode** pHead, int value) {
    if (*pHead == nullptr || pHead == nullptr)
        return;

    ListNode *pToDeleted = nullptr;
    if ((*pHead)->m_nValue == value) {
        pToDeleted = *pHead;
        *pHead = (*pHead)->m_pNext;
    }
    else {
        ListNode *pNode = *pHead;
        while (pNode->m_pNext != nullptr && pNode->m_pNext->m_nValue != value)
            pNode = pNode->m_pNext;
        if (pNode->m_pNext != nullptr && pNode->m_pNext->m_nValue == value) {
            pToDeleted = pNode->m_pNext;
            pNode->m_pNext = pNode->m_pNext->m_pNext;
        }
    }

    if (pToDeleted != nullptr) {
        delete pToDeleted;
        pToDeleted = nullptr;
    }
}

__declspec( dllexport )的作用为不用导入库文件，就可以在外部直接调用其后的函数功能。

例如：加入建一个test.cpp文件，导入List.h后可以直接调用其函数