header file - ＜typeinfo＞

水深无声 2023-03-06 05:59 4阅读 0赞

#  header file - <typeinfo> #

Type information - 类型信息

This header defines types used related to operators `typeid` and `dynamic_cast`.  
这个头文件定义了与操作符 `typeid` and `dynamic_cast` 相关的类型。

The inclusion of this header is required prior to any use of the `typeid` operator.  
在使用 `typeid` 运算符之前，必须包含此标头。

C++ 并没有规定 `typeid` 的实现标准，不同编译器可能会不一样。

## 1. Linux ##

### 1.1 cannot convert `‘std::shared_ptr<int>’` to `‘const int*’` ###

/*
    ============================================================================
    Name        : yongqiang.cpp
    Author      : Yongqiang Cheng
    Version     : Version 1.0.0
    Copyright   : Copyright (c) 2020 Yongqiang Cheng
    Description : Hello World in C++, Ansi-style
    ============================================================================
    */
    
    #include <iostream>
    #include <memory>
    #include <string>
    #include <typeinfo>
    
    void output(std::string msg, const int *pint) {
        std::cout << msg << *pint << "\n";
    }
    
    int main() {
        int *pint = new int(10);
        std::shared_ptr<int> pshared = std::make_shared<int>(9);
    
        std::cout << "data type: " << typeid(pint).name() << std::endl;
        std::cout << "data type (owned pointer): " << typeid(pshared).name() << std::endl;
        std::cout << "data type (stored pointer): " << typeid(pshared.get()).name() << std::endl;
        std::cout << "data: " << *pint << "\n";
        std::cout << "data (owned pointer): " << *pshared << "\n";
        std::cout << "data (stored pointer): " << *(pshared.get()) << "\n";
    
        output("Naked pointer: ", pint);
        output("Shared pointer ", pshared);
        output("Shared pointer with get(): ", pshared.get());
    
        delete pint;
    
        return 0;
    }

====================[ Build | yongqiang | Debug ]===============================
    /home/yongqiang/software/clion-2019.1.4/bin/cmake/linux/bin/cmake --build /home/yongqiang/CLionProjects/yongqiang/cmake-build-debug --target yongqiang -- -j 6
    Scanning dependencies of target yongqiang
    [ 50%] Building CXX object CMakeFiles/yongqiang.dir/main.cpp.o
    /home/yongqiang/CLionProjects/yongqiang/main.cpp: In function ‘int main()’:
    /home/yongqiang/CLionProjects/yongqiang/main.cpp:32:38: error: cannot convert ‘std::shared_ptr<int>’ to ‘const int*’ for argument ‘2’ to ‘void output(std::__cxx11::string, const int*)’
         output("Shared pointer ", pshared);
                                          ^
    CMakeFiles/yongqiang.dir/build.make:62: recipe for target 'CMakeFiles/yongqiang.dir/main.cpp.o' failed
    make[3]: *** [CMakeFiles/yongqiang.dir/main.cpp.o] Error 1
    CMakeFiles/Makefile2:72: recipe for target 'CMakeFiles/yongqiang.dir/all' failed
    make[2]: *** [CMakeFiles/yongqiang.dir/all] Error 2
    CMakeFiles/Makefile2:84: recipe for target 'CMakeFiles/yongqiang.dir/rule' failed
    make[1]: *** [CMakeFiles/yongqiang.dir/rule] Error 2
    Makefile:118: recipe for target 'yongqiang' failed
    make: *** [yongqiang] Error 2

### 1.2 `stored pointer` \- `owned pointer` ###

/*
    ============================================================================
    Name        : yongqiang.cpp
    Author      : Yongqiang Cheng
    Version     : Version 1.0.0
    Copyright   : Copyright (c) 2020 Yongqiang Cheng
    Description : Hello World in C++, Ansi-style
    ============================================================================
    */
    
    #include <iostream>
    #include <memory>
    #include <string>
    #include <typeinfo>
    
    void output(std::string msg, const int *pint) {
        std::cout << msg << *pint << "\n";
    }
    
    int main() {
        int *pint = new int(10);
        std::shared_ptr<int> pshared = std::make_shared<int>(9);
    
        std::cout << "data type: " << typeid(pint).name() << std::endl;
        std::cout << "data type (owned pointer): " << typeid(pshared).name() << std::endl;
        std::cout << "data type (stored pointer): " << typeid(pshared.get()).name() << std::endl;
        std::cout << "data: " << *pint << "\n";
        std::cout << "data (owned pointer): " << *pshared << "\n";
        std::cout << "data (stored pointer): " << *(pshared.get()) << "\n";
    
        output("Naked pointer: ", pint);
    //    output("Shared pointer ", pshared);
        output("Shared pointer with get(): ", pshared.get());
    
        delete pint;
    
        return 0;
    }

/home/yongqiang/CLionProjects/yongqiang/cmake-build-debug/yongqiang
    data type: Pi
    data type (owned pointer): St10shared_ptrIiE
    data type (stored pointer): Pi
    data: 10
    data (owned pointer): 9
    data (stored pointer): 9
    Naked pointer: 10
    Shared pointer with get(): 9
    
    Process finished with exit code 0

## 2. Windows ##

### 2.1 cannot convert argument 2 from `'std::shared_ptr<int>'` to `'const int *'` ###

/*
    ============================================================================
    Name        : yongqiang.cpp
    Author      : Yongqiang Cheng
    Version     : Version 1.0.0
    Copyright   : Copyright (c) 2020 Yongqiang Cheng
    Description : Hello World in C++, Ansi-style
    ============================================================================
    */
    
    #include <iostream>
    #include <memory>
    #include <string>
    #include <typeinfo>
    
    void output(std::string msg, const int *pint) {
    	std::cout << msg << *pint << "\n";
    }
    
    int main() {
    	int *pint = new int(10);
    	std::shared_ptr<int> pshared = std::make_shared<int>(9);
    
    	std::cout << "data type: " << typeid(pint).name() << std::endl;
    	std::cout << "data type (owned pointer): " << typeid(pshared).name() << std::endl;
    	std::cout << "data type (stored pointer): " << typeid(pshared.get()).name() << std::endl;
    	std::cout << "data: " << *pint << "\n";
    	std::cout << "data (owned pointer): " << *pshared << "\n";
    	std::cout << "data (stored pointer): " << *(pshared.get()) << "\n";
    
    	output("Naked pointer: ", pint);
    	output("Shared pointer ", pshared);
    	output("Shared pointer with get(): ", pshared.get());
    
    	delete pint;
    
    	return 0;
    }

1>------ Build started: Project: yongqiangcheng, Configuration: Debug Win32 ------
    1>  yongqiang.cpp
    1>d:\visual_studio_workspace\yongqiangcheng\yongqiangcheng\yongqiang.cpp(32): error C2664: 'void output(std::string,const int *)': cannot convert argument 2 from 'std::shared_ptr<int>' to 'const int *'
    1>  d:\visual_studio_workspace\yongqiangcheng\yongqiangcheng\yongqiang.cpp(32): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
    ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

### 2.2 `stored pointer` \- `owned pointer` ###

/*
    ============================================================================
    Name        : yongqiang.cpp
    Author      : Yongqiang Cheng
    Version     : Version 1.0.0
    Copyright   : Copyright (c) 2020 Yongqiang Cheng
    Description : Hello World in C++, Ansi-style
    ============================================================================
    */
    
    #include <iostream>
    #include <memory>
    #include <string>
    #include <typeinfo>
    
    void output(std::string msg, const int *pint) {
    	std::cout << msg << *pint << "\n";
    }
    
    int main() {
    	int *pint = new int(10);
    	std::shared_ptr<int> pshared = std::make_shared<int>(9);
    
    	std::cout << "data type: " << typeid(pint).name() << std::endl;
    	std::cout << "data type (owned pointer): " << typeid(pshared).name() << std::endl;
    	std::cout << "data type (stored pointer): " << typeid(pshared.get()).name() << std::endl;
    	std::cout << "data: " << *pint << "\n";
    	std::cout << "data (owned pointer): " << *pshared << "\n";
    	std::cout << "data (stored pointer): " << *(pshared.get()) << "\n";
    
    	output("Naked pointer: ", pint);
    	// output("Shared pointer ", pshared);
    	output("Shared pointer with get(): ", pshared.get());
    
    	delete pint;
    
    	return 0;
    }

data type: int *
    data type (owned pointer): class std::shared_ptr<int>
    data type (stored pointer): int *
    data: 10
    data (owned pointer): 9
    data (stored pointer): 9
    Naked pointer: 10
    Shared pointer with get(): 9
    请按任意键继续. . .

## References ##

[http://www.cplusplus.com/reference/typeinfo/][http_www.cplusplus.com_reference_typeinfo]

[http_www.cplusplus.com_reference_typeinfo]: http://www.cplusplus.com/reference/typeinfo/