C++ - `std::shared_ptr::get`

public member function - 公开成员函数
Defined in header <memory> - 定义于头文件 <memory>

1. `std::shared_ptr::get`

element_type* get() const noexcept;

Get pointer.
获取指针。

Returns the stored pointer.
返回存储的指针。

The stored pointer points to the object the shared_ptr object dereferences to, which is generally the same as its owned pointer.
存储的指针指向 shared_ptr 对象解引用的对象，通常与其拥有的指针相同。

The stored pointer (i.e., the pointer returned by this function) may not be the owned pointer (i.e., the pointer deleted on object destruction) if the shared_ptr object is an alias (i.e., alias-constructed objects and their copies).
如果 shared_ptr 对象是别名 (i.e., alias-constructed objects and their copies)，则 stored pointer (i.e., the pointer returned by this function) 可能不是 owned pointer (i.e., the pointer deleted on object destruction)。

A shared_ptr may share ownership of an object while storing a pointer to another object. get() returns the stored pointer, not the managed pointer.
shared_ptr 可以在存储指向另一个对象的指针时共享对象的所有权。get() 返回存储的指针，而非被管理指针。

2. Parameters

none

3. Return value

The stored pointer.
element_type is a member type, alias of shared_ptr's template parameter (T).

4. Examples

4.1 `std::shared_ptr::get`

//============================================================================
// Name        : std::shared_ptr::get
// Author      : Yongqiang Cheng
// Version     : Version 1.0.0
// Copyright   : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================#include <iostream>
#include <memory>int main()
{int* p = new int(10);std::shared_ptr<int> strong(p);if (strong.get() == p)std::cout << "strong and p point to the same location\n";// four ways of accessing the same address:std::cout << *strong.get() << "\n";std::cout << *(strong.get()) << "\n";std::cout << *strong << "\n";std::cout << *p << "\n";return 0;
}

strong and p point to the same location
10
10
10
10
请按任意键继续. . .

assignment [ə'saɪnmənt]：n. 任务，布置，赋值

4.2 `std::shared_ptr::get`

//============================================================================
// Name        : std::shared_ptr::get
// Author      : Yongqiang Cheng
// Version     : Version 1.0.0
// Copyright   : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================#include <iostream>
#include <memory>void output(std::string msg, int const* pint)
{std::cout << msg << *pint << "\n";
}int main()
{int* pint = new int(10);std::shared_ptr<int> pshared = std::make_shared<int>(9);output("Naked pointer: ", pint);// output("Shared pointer ", pshared); // 编译错误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(14): error C2679: binary '<<': no operator found which takes a right-hand operand of type 'std::string' (or there is no acceptable conversion)
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(495): note: could be 'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_streambuf<char,std::char_traits<char>> *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(475): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(const void *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(455): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long double)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(435): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(double)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(415): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(float)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(395): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned __int64)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(375): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(__int64)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(355): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned long)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(335): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(long)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(315): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned int)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(290): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(int)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(270): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(unsigned short)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(236): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(short)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(216): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(bool)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(209): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::ios_base &(__cdecl *)(std::ios_base &))'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(202): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ios<char,std::char_traits<char>> &(__cdecl *)(std::basic_ios<char,std::char_traits<char>> &))'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(196): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(std::basic_ostream<char,std::char_traits<char>> &(__cdecl *)(std::basic_ostream<char,std::char_traits<char>> &))'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(692): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(739): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(777): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const char *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(824): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,char)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(950): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const signed char *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(957): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,signed char)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(964): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const unsigned char *)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(971): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,unsigned char)'
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(981): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>,std::string>(std::basic_ostream<char,std::char_traits<char>> &&,const _Ty &)'
1>          with
1>          [
1>              _Ty=std::string
1>          ]
1>  d:\program files (x86)\microsoft visual studio 14.0\vc\include\ostream(1019): note: or       'std::basic_ostream<char,std::char_traits<char>> &std::operator <<<char,std::char_traits<char>>(std::basic_ostream<char,std::char_traits<char>> &,const std::error_code &)'
1>  d:\visual_studio_workspace\yongqiangcheng\yongqiangcheng\yongqiang.cpp(14): note: while trying to match the argument list '(std::ostream, std::string)'
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

添加头文件 #include <string>。

//============================================================================
// Name        : std::shared_ptr::get
// Author      : Yongqiang Cheng
// Version     : Version 1.0.0
// Copyright   : Copyright (c) 2019 Yongqiang Cheng
// Description : Hello World in C++, Ansi-style
//============================================================================#include <iostream>
#include <memory>
#include <string>void output(std::string msg, int const* pint)
{std::cout << msg << *pint << "\n";
}int main()
{int* pint = new int(10);std::shared_ptr<int> pshared = std::make_shared<int>(9);output("Naked pointer: ", pint);// output("Shared pointer ", pshared); // 编译错误output("Shared pointer with get(): ", pshared.get());delete pint;return 0;
}

Naked pointer: 10
Shared pointer with get(): 9
请按任意键继续. . .

4.3 `stored pointer` - `owned pointer`

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

/*
============================================================================
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;
}

Linux

/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(): 9Process finished with exit code 0

Windows

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/memory/shared_ptr/get/
https://en.cppreference.com/w/cpp/memory/shared_ptr/get