C++ - std::shared_ptr::get
std::shared_ptr::getpublic member function - 公開成員函數
Defined in header <memory> - 定義於頭文件 <memory>
1. std::shared_ptr::get
element_type* get() const noexcept;
Get pointer.
獲取指針。
Returns the stored pointer.
返回存儲的指針。
The stored pointer points to the object the shared_ptr object dereferences to, which is generally the same as its owned pointer.
存儲的指針指向 shared_ptr 對象解引用的對象，通常與其擁有的指針相同。
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 對象是別名 (i.e., alias-constructed objects and their copies)，則 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 可以在存儲指向另一個對象的指針時共享對象的所有權。get() 返回存儲的指針，而非被管理指針。
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
請按任意鍵繼續. . .
assignment [ə'saɪnmənt]：n. 任務，佈置，賦值
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); // 編譯錯誤
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 ==========
添加頭文件 #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); // 編譯錯誤
output("Shared pointer with get(): ", pshared.get());
delete pint;
return 0;
}
Naked pointer: 10
Shared pointer with get(): 9
請按任意鍵繼續. . .
References
http://www.cplusplus.com/reference/memory/shared_ptr/get/
https://en.cppreference.com/w/cpp/memory/shared_ptr/get