visual-c++ - 要求对 VC++ 进行有关插入和安放的调查

Question

我正在调查 vector 的以下成员函数中执行了多少特殊成员函数:

insert
emplace
push_back
emplace_back

在各种运行时间条件下。我的目的是发表一篇论文，将这些成员函数相互比较，以及 std::lib 的每个 c++11 实现:libstdc++、libc++ 和 vc++，并就何时最好提供建议使用每个成员函数(当有多个选择时)。我有关于 libc++ 和 libstdc++-4.8 的数据，但我缺少关于 vc++ 的数据。

我正在寻找有关 vc++ 的答案，其中包括 vc++ 版本号(2010、2012、2013)。我的目的是就何时应该优先考虑这些成员中的每一个，并根据现实世界的经验提供建议。我将对每个 vc++ 版本的第一个响应进行投票。我的意图不是抨击任何特定平台。但是，如果我的结果鼓励任何现有平台在 future 改进，那就太糟糕了。

我想看到的测试结果是:

#include <iostream>
#include <vector>

class X
{
    int i_;
    int* p_;

public:
    struct special
    {
        unsigned c;
        unsigned dt;
        unsigned cc;
        unsigned ca;
        unsigned mc;
        unsigned ma;
    };
    static special sp;

    X(int i, int* p)
        : i_(i)
        , p_(p)
    {
//         std::cout << "X(int i, int* p)\n";
        sp.c++;
    }

    ~X()
    {
//         std::cout << "~X()\n";
        sp.dt++;
    }

    X(const X& x)
        : i_(x.i_)
        , p_(x.p_)
    {
//         std::cout << "X(const X& x)\n";
        sp.cc++;
    }

    X& operator=(const X& x)
    {

        i_ = x.i_;
        p_ = x.p_;
//         std::cout << "X& operator=(const X& x)\n";
        sp.ca++;
        return *this;
    }

    X(X&& x) noexcept
        : i_(x.i_)
        , p_(x.p_)
    {
//         std::cout << "X(X&& x)\n";
        sp.mc++;
    }

    X& operator=(X&& x) noexcept
    {

        i_ = x.i_;
        p_ = x.p_;
//         std::cout << "X& operator=(X&& x)\n";
        sp.ma++;
        return *this;
    }

};

std::ostream&
operator<<(std::ostream& os, X::special const& sp)
{
    os << sp.c << '\n';
    os << sp.dt << '\n';
    os << sp.cc << '\n';
    os << sp.ca << '\n';
    os << sp.mc << '\n';
    os << sp.ma << '\n';
    return os;
}

X::special X::sp{};

int
main()
{
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--insert lvalue no reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace lvalue no reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--insert xvalue no reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace xvalue no reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--insert rvalue no reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--emplace rvalue no reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--insert lvalue reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace lvalue reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--insert xvalue reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace xvalue reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--insert rvalue reallocation--\n";
        X::sp = {};
        v.insert(v.begin(), X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--emplace rvalue reallocation--\n";
        X::sp = {};
        v.emplace(v.begin(), X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }

    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--push_back lvalue no reallocation--\n";
        X::sp = {};
        v.push_back(x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace_back lvalue no reallocation--\n";
        X::sp = {};
        v.emplace_back(x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--push_back xvalue no reallocation--\n";
        X::sp = {};
        v.push_back(std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace_back xvalue no reallocation--\n";
        X::sp = {};
        v.emplace_back(std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--push_back rvalue no reallocation--\n";
        X::sp = {};
        v.push_back(X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(4);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--emplace_back rvalue no reallocation--\n";
        X::sp = {};
        v.emplace_back(X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--push_back lvalue reallocation--\n";
        X::sp = {};
        v.push_back(x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace_back lvalue reallocation--\n";
        X::sp = {};
        v.emplace_back(x);
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--push_back xvalue reallocation--\n";
        X::sp = {};
        v.push_back(std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        X x{0,0};
        std::cout << "--emplace_back xvalue reallocation--\n";
        X::sp = {};
        v.emplace_back(std::move(x));
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--push_back rvalue reallocation--\n";
        X::sp = {};
        v.push_back(X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
    {
        std::vector<X> v;
        v.reserve(3);
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        v.push_back(X(0,0));
        std::cout << "--emplace_back rvalue reallocation--\n";
        X::sp = {};
        v.emplace_back(X{0,0});
        std::cout << X::sp;
        std::cout << "----\n";
    }
}

例如，这里是 gcc-4.8 上这个测试的输出: https://ideone.com/imAMnU

如果有人发现 4.8 之后的 gcc 版本的结果不同并且想要提供这些结果，那也将受到赞赏(并赞成)。如果我无法区分哪些等效的响应首先出现，我很高兴为所有这些响应提供支持。但是，此时我不确定如何为这项调查选择正确的答案。

在我可能发表的任何内容中，数据的贡献者肯定会得到感谢。我也很高兴在这个问题中发布一个链接，指向将来可能从这些数据中得出的任何结论。

总之，我意识到这种风格的问题不是 SO 的常态。然而，它是本着促进 C++ 社区的公共(public)知识的精神提出的，并且尽可能地透明。如果人们出于任何原因想要结束这个问题，我接受这一点，但我个人认为这不符合 C++ 社区的最佳利益。

更新

这是我所说的使这项调查成为可能的论文:

insert vs emplace

Answer 1

使用 Release 模式编译的 VS2012 代码。

命令

cl/O2/EHsc/W4 Console_12.cpp

输出

--insert lvalue no reallocation--    
4        
4        
1        
3        
4  
0           
----    
--emplace lvalue no reallocation--    
8    
15    
2    
3    
10    
6    
----    
--insert xvalue no reallocation--    
12    
26    
2    
3    
17    
12    
----    
--emplace xvalue no reallocation--    
16    
37    
2    
3    
24    
18    
----    
--insert rvalue no reallocation--    
20    
49    
2    
3    
31    
24    
----    
--emplace rvalue no reallocation--    
24    
60    
2    
3    
38    
30    
----    
--insert lvalue reallocation--    
28    
70    
3    
3    
44    
30    
----    
--emplace lvalue reallocation--    
32    
84    
4    
3    
53    
36    
----    
--insert xvalue reallocation--    
36    
98    
4    
3    
63    
42    
----    
--emplace xvalue reallocation--    
40    
112    
4    
3    
73    
48    
----    
--insert rvalue reallocation--    
44    
127    
4    
3    
83    
54    
----    
--emplace rvalue reallocation--    
48    
141    
4    
3    
93    
60    
----    
--push_back lvalue no reallocation--    
52    
148    
5    
3    
96    
60    
----    
--emplace_back lvalue no reallocation--    
56    
156    
6    
3    
99    
60    
----    
--push_back xvalue no reallocation--    
60    
164    
6    
3    
103    
60    
----    
--emplace_back xvalue no reallocation--    
64    
172    
6    
3    
107    
60    
----    
--push_back rvalue no reallocation--    
68    
181    
6    
3    
111    
60    
----    
--emplace_back rvalue no reallocation--    
72    
189    
6    
3    
115    
60    
----    
--push_back lvalue reallocation--    
76    
199    
7    
3    
121    
60    
----    
--emplace_back lvalue reallocation--    
80    
210    
8    
3    
127    
60    
----    
--push_back xvalue reallocation--    
84    
221    
8    
3    
134    
60    
----    
--emplace_back xvalue reallocation--    
88    
232    
8    
3    
141    
60    
----    
--push_back rvalue reallocation--    
92    
244    
8    
3    
148    
60    
----    
--emplace_back rvalue reallocation--    
96    
255    
8    
3    
155    
60    
----