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添加 so 共享库、Windows 应用程序入口、Windows 动态链接库
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README.md
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README.md
@ -2594,41 +2594,377 @@ Linux 下的共享库就是普通的 ELF 共享对象。
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* `LD_PRELOAD`：指定预先装载的一些共享库甚至是目标文件
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* `LD_DEBUG`：打开动态链接器的调试功能
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### Windows 的动态链接库（Dynamic-Link Library）
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#### so 共享库的编写
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<details><summary>Windows 动态链接库例子</summary>
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<details><summary>使用 CLion 编写共享库</summary>
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创建一个名为 MySharedLib 的共享库
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CMakeLists.txt
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```cmake
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cmake_minimum_required(VERSION 3.10)
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project(MySharedLib)
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set(CMAKE_CXX_STANDARD 11)
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add_library(MySharedLib SHARED library.cpp library.h)
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```
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library.h
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DLL 头文件
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```cpp
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#ifdef __cplusplus
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extern "C" {
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#endif
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#ifndef MYSHAREDLIB_LIBRARY_H
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#define MYSHAREDLIB_LIBRARY_H
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#ifdef _WIN32
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# ifdef MODULE_API_EXPORTS
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# define MODULE_API __declspec(dllexport)
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# else
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# define MODULE_API __declspec(dllimport)
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# endif
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#else
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# define MODULE_API
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#endif
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// 打印 Hello World!
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void hello();
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MODULE_API int module_init();
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#ifdef __cplusplus
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// 使用可变模版参数求和
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template <typename T>
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T sum(T t)
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{
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return t;
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}
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template <typename T, typename ...Types>
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T sum(T first, Types ... rest)
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{
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return first + sum<T>(rest...);
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}
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#endif
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```
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DLL 源文件
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```cpp
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#define MODULE_API_EXPORTS
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#include "module.h"
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library.cpp
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MODULE_API int module_init()
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```cpp
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#include <iostream>
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#include "library.h"
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void hello() {
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std::cout << "Hello, World!" << std::endl;
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}
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```
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</details>
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#### so 共享库的使用（被可执行项目调用）
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<details><summary>使用 CLion 调用共享库</summary>
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创建一个名为 TestSharedLib 的可执行项目
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CMakeLists.txt
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```cmake
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cmake_minimum_required(VERSION 3.10)
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project(TestSharedLib)
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# C++11 编译
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set(CMAKE_CXX_STANDARD 11)
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# 头文件路径
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set(INC_DIR /home/xx/code/clion/MySharedLib)
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# 库文件路径
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set(LIB_DIR /home/xx/code/clion/MySharedLib/cmake-build-debug)
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include_directories(${INC_DIR})
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link_directories(${LIB_DIR})
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link_libraries(MySharedLib)
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add_executable(TestSharedLib main.cpp)
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# 链接 MySharedLib 库
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target_link_libraries(TestSharedLib MySharedLib)
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```
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main.cpp
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```cpp
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#include <iostream>
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#include "library.h"
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using std::cout;
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using std::endl;
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int main() {
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hello();
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cout << "1 + 2 = " << sum(1,2) << endl;
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cout << "1 + 2 + 3 = " << sum(1,2,3) << endl;
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return 0;
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}
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```
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执行结果
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```
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Hello, World!
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1 + 2 = 3
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1 + 2 + 3 = 6
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```
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</details>
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### Windows 应用程序入口函数
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* GUI（Graphical User Interface）应用，链接器选项：`/SUBSYSTEM:WINDOWS`
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* CUI（Console User Interface）应用，链接器选项：`/SUBSYSTEM:CONSOLE`
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<details><summary>_tWinMain 与 _tmain 函数声明</summary>
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```cpp
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Int WINAPI _tWinMain(
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HINSTANCE hInstanceExe,
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HINSTANCE,
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PTSTR pszCmdLine,
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int nCmdShow);
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int _tmain(
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int argc,
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TCHAR *argv[],
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TCHAR *envp[]);
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```
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</details>
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应用程序类型|入口点函数|嵌入可执行文件的启动函数
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---|---|---
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处理ANSI字符（串）的GUI应用程序|_tWinMain(WinMain)|WinMainCRTSartup
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处理Unicode字符（串）的GUI应用程序|_tWinMain(wWinMain)|wWinMainCRTSartup
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处理ANSI字符（串）的CUI应用程序|_tmain(Main)|mainCRTSartup
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处理Unicode字符（串）的CUI应用程序|_tmain(wMain)|wmainCRTSartup
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动态链接库（Dynamic-Link Library）|DllMain|_DllMainCRTStartup
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### Windows 的动态链接库（Dynamic-Link Library）
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#### 用处
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* 扩展了应用程序的特性
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* 简化了项目管理
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* 有助于节省内存
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* 促进了资源的共享
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* 促进了本地化
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* 有助于解决平台间的差异
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* 可以用于特殊目的
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#### 注意
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* 创建 DLL，事实上是在创建可供一个可执行模块调用的函数
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* 当一个模块提供一个内存分配函数（malloc、new）的时候，它必须同时提供另一个内存释放函数（free、delete）
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* 在使用 C 和 C++ 混编的时候，要使用 extern "C" 修饰符
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* 一个 DLL 可以导出函数、变量（避免导出）、C++ 类（导出导入需要同编译器，否则避免导出）
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* DLL 模块：cpp 文件中的 __declspec(dllexport) 写在 include 头文件之前
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* 调用 DLL 的可执行模块：cpp 文件的 __declspec(dllimport) 之前不应该定义 MYLIBAPI
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#### 加载 Windows 程序的搜索顺序
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1. 包含可执行文件的目录
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2. Windows 的系统目录，可以通过 GetSystemDirectory 得到
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3. 16 位的系统目录，即 Windows 目录中的 System 子目录
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4. Windows 目录，可以通过 GetWindowsDirectory 得到
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5. 进程的当前目录
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6. PATH 环境变量中所列出的目录
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#### DLL 入口函数
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<details><summary>DllMain 函数</summary>
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```cpp
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BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
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{
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/* do something useful */
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switch(fdwReason)
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{
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case DLL_PROCESS_ATTACH:
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// 第一次将一个DLL映射到进程地址空间时调用
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// The DLL is being mapped into the process' address space.
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break;
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case DLL_THREAD_ATTACH:
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// 当进程创建一个线程的时候，用于告诉DLL执行与线程相关的初始化（非主线程执行）
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// A thread is bing created.
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break;
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case DLL_THREAD_DETACH:
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// 系统调用 ExitThread 线程退出前，即将终止的线程通过告诉DLL执行与线程相关的清理
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// A thread is exiting cleanly.
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break;
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case DLL_PROCESS_DETACH:
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// 将一个DLL从进程的地址空间时调用
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// The DLL is being unmapped from the process' address space.
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break;
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}
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return (TRUE); // Used only for DLL_PROCESS_ATTACH
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}
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```
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</details>
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#### 载入卸载库
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<details><summary>LoadLibrary、LoadLibraryExA、LoadPackagedLibrary、FreeLibrary、FreeLibraryAndExitThread 函数声明</summary>
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```cpp
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// 载入库
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HMODULE WINAPI LoadLibrary(
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_In_ LPCTSTR lpFileName
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);
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HMODULE LoadLibraryExA(
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LPCSTR lpLibFileName,
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HANDLE hFile,
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DWORD dwFlags
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);
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// 若要在通用 Windows 平台（UWP）应用中加载 Win32 DLL，需要调用 LoadPackagedLibrary，而不是 LoadLibrary 或 LoadLibraryEx
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HMODULE LoadPackagedLibrary(
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LPCWSTR lpwLibFileName,
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DWORD Reserved
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);
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// 卸载库
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BOOL WINAPI FreeLibrary(
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_In_ HMODULE hModule
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);
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// 卸载库和退出线程
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VOID WINAPI FreeLibraryAndExitThread(
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_In_ HMODULE hModule,
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_In_ DWORD dwExitCode
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);
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```
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</details>
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#### 显示地链接到导出符号
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<details><summary>GetProcAddress 函数声明</summary>
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```cpp
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FARPROC GetProcAddress(
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HMODULE hInstDll,
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PCSTR pszSymbolName // 只能接受 ANSI 字符串，不能是 Unicode
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);
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```
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</details>
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#### DumpBin.exe 查看 DLL 信息
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在 `VS 的开发人员命令提示符` 使用 `DumpBin.exe` 可查看 DLL 库的导出段（导出的变量、函数、类名的符号）、相对虚拟地址（RVA，relative virtual address）。如：
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```
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DUMPBIN -exports D:\mydll.dll
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```
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#### LoadLibrary 与 FreeLibrary 流程图
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<details><summary>LoadLibrary 与 FreeLibrary 流程图</summary>
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##### LoadLibrary
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##### FreeLibrary
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</details>
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#### DLL 库的编写（导出一个 DLL 模块）
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<details><summary>DLL 库的编写（导出一个 DLL 模块）</summary>
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DLL 头文件
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```cpp
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// MyLib.h
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#ifdef MYLIBAPI
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// MYLIBAPI 应该在全部 DLL 源文件的 include "Mylib.h" 之前被定义
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// 全部函数/变量正在被导出
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#else
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// 这个头文件被一个exe源代码模块包含，意味着全部函数/变量被导入
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#define MYLIBAPI extern "C" __declspec(dllimport)
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#endif
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// 这里定义任何的数据结构和符号
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// 定义导出的变量（避免导出变量）
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MYLIBAPI int g_nResult;
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// 定义导出函数原型
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MYLIBAPI int Add(int nLeft, int nRight);
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```
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DLL 源文件
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```cpp
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// MyLibFile1.cpp
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// 包含标准Windows和C运行时头文件
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#include <windows.h>
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// DLL源码文件导出的函数和变量
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#define MYLIBAPI extern "C" __declspec(dllexport)
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// 包含导出的数据结构、符号、函数、变量
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#include "MyLib.h"
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// 将此DLL源代码文件的代码放在此处
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int g_nResult;
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int Add(int nLeft, int nRight)
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{
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g_nResult = nLeft + nRight;
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return g_nResult;
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}
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```
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</details>
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#### DLL 库的使用（运行时动态链接 DLL）
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<details><summary>DLL 库的使用（运行时动态链接 DLL）</summary>
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```cpp
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// A simple program that uses LoadLibrary and
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// GetProcAddress to access myPuts from Myputs.dll.
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#include <windows.h>
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#include <stdio.h>
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typedef int (__cdecl *MYPROC)(LPWSTR);
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int main( void )
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{
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HINSTANCE hinstLib;
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MYPROC ProcAdd;
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BOOL fFreeResult, fRunTimeLinkSuccess = FALSE;
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// Get a handle to the DLL module.
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hinstLib = LoadLibrary(TEXT("MyPuts.dll"));
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// If the handle is valid, try to get the function address.
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if (hinstLib != NULL)
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{
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ProcAdd = (MYPROC) GetProcAddress(hinstLib, "myPuts");
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// If the function address is valid, call the function.
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if (NULL != ProcAdd)
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{
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fRunTimeLinkSuccess = TRUE;
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(ProcAdd) (L"Message sent to the DLL function\n");
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}
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// Free the DLL module.
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fFreeResult = FreeLibrary(hinstLib);
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}
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// If unable to call the DLL function, use an alternative.
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if (! fRunTimeLinkSuccess)
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printf("Message printed from executable\n");
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return 0;
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}
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```
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