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示例执行

示例输出

/Users/luogw/CLionProjects/untitled2/cmake-build-debug/untitled2construct, call ResManger() // 库的全局变量construct, call GlobalClass()2construct, call GlobalClass()call main()Hello, World! // 库的hello函数的输出construct, call CommonClass()register atexitnext line call exit(0)atexit callback, lambda expressionatexit callback, beforeExitF()destruct, call ~GlobalClass()destruct, call ~GlobalClass()2destruct, call ~ResManger()Process finished with exit code 0

对应的可执行程序的源代码如下

#include 
   
    #include 
    
     #include "lib/include/library.h"using namespace std;class GlobalClass {public:    GlobalClass() {        cout << "construct, call GlobalClass()" << endl;    }    ~GlobalClass() {        cout << "destruct, call ~GlobalClass()" << endl;    }};class GlobalClass2 {public:    GlobalClass2() {        cout << "construct, call GlobalClass()2" << endl;    }    ~GlobalClass2() {        cout << "destruct, call ~GlobalClass()2" << endl;    }};class CommonClass {public:    CommonClass() {        cout << "construct, call CommonClass()" << endl;    }    ~CommonClass() {        cout << "destruct, call  ~CommonClass()" << endl;    }};//全局对象GlobalClass2 G_Class2;GlobalClass G_Class;void beforeExitF() {    cout << "atexit callback, beforeExitF()" << endl;}int main() {    cout << "call main()" << endl;    // 调用动态库的方法    hello();    CommonClass commonClass;    cout << "register atexit" << endl;    //注册应用退出时的回调方法    atexit(beforeExitF);    //注删应用退出前的回调lamdba表达式    atexit([] {        cout << "atexit callback, lambda expression" << endl;    });    //ateixt是FILO的原侧，先进后出，即后注册的先执行    cout << "next line call exit(0)" << endl;    /*     * 这时调exit提前结束了进程，所以CommonClass的析构方法不会调到，因为main没有执行return，即main没有出栈     * exit跟return的区别，具体看这里的讨认 https://www.zhihu.com/question/26591968     */    exit(0);//    return 0;}
    
   

知识点

• 一个可执行程序的全局变量在main方法执行之前构造/初始化，在应用退出前析构。全局变量包括执行程序和其依赖的库定义的全局变量，库包括静态库和动态库。
• 全局变量的构造与析构是配对的，但先构造的会后析构。库定义的全局变量比可执行的全局变量要先构造。
• 全局变量初始化的顺序跟其在源文件中定义的位置一致，定义在前面先得到构造
• atexit的可执行代码段的注册与执行是FILO的规则，即后注册的先执行。这也就办什么全局变量先构造的后析造的原因。全局变量的析构是利用atexit实现（编译器帮我们做的）

代码说明

• 示例的运行环境是macOS，IDE 是Clion，代码构建是Clion默认的Cmake
• 示例为一个可执行程序工程跟一个动态库工程，动态库构建后产物（动态库文件还有头文件）拷贝到可执行程序工程根目录下的lib目录

动态库项目

#ifndef UNTITLED1_LIBRARY_H#define UNTITLED1_LIBRARY_Hvoid hello();#endif //UNTITLED1_LIBRARY_H

library.cpp

#include "library.h"#include 
   
    using namespace std;class ResManger {public:    ResManger() {        cout << "construct, call ResManger()" << endl;    }    ~ResManger() {        cout << "destruct, call ~ResManger()" << endl;    }};ResManger resManger;void hello() {    std::cout << "Hello, World!" << std::endl;}
   

CMakeLists.txt

cmake_minimum_required(VERSION 3.17)project(untitled1)set(CMAKE_CXX_STANDARD 14)add_library(untitled1 SHARED library.cpp library.h)

其它的默认配置，可以用otool来看一下动态库使用时的路径配置情况

$ otool -L cmake-build-debug/libuntitled1.dylib            cmake-build-debug/libuntitled1.dylib:        @rpath/libuntitled1.dylib (compatibility version 0.0.0, current version 0.0.0)        /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 904.4.0)        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1292.60.1)

可执行程序工程

#include 
   
    #include 
    
     #include "lib/include/library.h"using namespace std;class GlobalClass {public:    GlobalClass() {        cout << "construct, call GlobalClass()" << endl;    }    ~GlobalClass() {        cout << "destruct, call ~GlobalClass()" << endl;    }};class GlobalClass2 {public:    GlobalClass2() {        cout << "construct, call GlobalClass()2" << endl;    }    ~GlobalClass2() {        cout << "destruct, call ~GlobalClass()2" << endl;    }};class CommonClass {public:    CommonClass() {        cout << "construct, call CommonClass()" << endl;    }    ~CommonClass() {        cout << "destruct, call  ~CommonClass()" << endl;    }};//全局对象GlobalClass2 G_Class2;GlobalClass G_Class;void beforeExitF() {    cout << "atexit callback, beforeExitF()" << endl;}int main() {    cout << "call main()" << endl;    // 调用动态库的方法    hello();    CommonClass commonClass;    cout << "register atexit" << endl;    //注册应用退出时的回调方法    atexit(beforeExitF);    //注删应用退出前的回调lamdba表达式    atexit([] {        cout << "atexit callback, lambda expression" << endl;    });    //ateixt是FILO的原侧，先进后出，即后注册的先执行    cout << "next line call exit(0)" << endl;    /*     * 这时调exit提前结束了进程，所以CommonClass的析构方法不会调到，因为main没有执行return，即main没有出栈     * exit跟return的区别，具体看这里的讨认 https://www.zhihu.com/question/26591968     */    exit(0);//    return 0;}
    
   

CMakeLists.txt

cmake_minimum_required(VERSION 3.17)project(untitled2)set(CMAKE_CXX_STANDARD 14)//添加动态库链接的路径link_libraries("${CMAKE_CURRENT_SOURCE_DIR}/lib/libuntitled1.dylib")add_executable(untitled2 main.cpp)

用otool查看可执行程序依赖的动态库的路径如下

# luogw @ ericluodeMacBook-Pro in ~/CLionProjects/untitled2 [17:13:12] $ otool -l cmake-build-debug/untitled2 | grep path         name @rpath/libuntitled1.dylib (offset 24)         path /Users/luogw/CLionProjects/untitled2/lib (offset 12)

参考资料

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