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c++ - Visual C++ 2017（版本 15.9.3）中的看似错误

问题描述

在 Visual C++ 2013 和http://cpp.sh上的 C++14 标准中有以下代码可以编译和运行良好。但是，在 Visual C++ 2017（ver 15.9.3）上，它给出了一条错误消息......这可能是一个错误？

代码是：

#include <vector>
#include <algorithm>
#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
    vector<long> v1 = {1}, v2 = {9};

    swap<vector<long>>(v1, v2);

    cout << "v1.front(): " << v1.front() << endl;
    cout << "v2.front(): " << v2.front() << endl;

    return 0;
}

我应该注意，如果我注释掉 swap() 函数，那么它可以编译并运行正常。错误消息都是由调用 swap() 产生的。

错误消息是：

地图测试.cpp

C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2048): error C2039: '_Alloc': is not a member of 'std::vector<long,std::allocator<_Ty>>'
        with
        [
            _Ty=long
        ]
maptest.cpp(9): note: see declaration of 'std::vector<long,std::allocator<_Ty>>'
        with
        [
            _Ty=long
        ]
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2096): note: see reference to class template instantiation 'std::_Vb_iter_base<_Alvbase_wrapped>' being compiled
        with
        [
            _Alvbase_wrapped=std::vector<long,std::allocator<long>>
        ]
maptest.cpp(11): note: see reference to class template instantiation 'std::_Vb_reference<std::vector<long,std::allocator<_Ty>>>' being compiled
        with
        [
            _Ty=long
        ]
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2048): error C2061: syntax error: identifier '_Alloc'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2049): error C2065: '_Alvbase': undeclared identifier
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2049): error C2923: 'std::allocator_traits': '_Alvbase' is not a valid template type argument for parameter '_Alloc'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2049): error C2955: 'std::allocator_traits': use of class template requires template argument list
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\xmemory0(903): note: see declaration of 'std::allocator_traits'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2049): error C2039: 'size_type': is not a member of 'std::allocator_traits<_Alloc>'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2049): error C2061: syntax error: identifier 'size_type'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2050): error C2065: '_Alvbase': undeclared identifier
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2050): error C2923: 'std::allocator_traits': '_Alvbase' is not a valid template type argument for parameter '_Alloc'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2050): error C2955: 'std::allocator_traits': use of class template requires template argument list
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\xmemory0(903): note: see declaration of 'std::allocator_traits'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2050): error C2039: 'difference_type': is not a member of 'std::allocator_traits<_Alloc>'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2050): error C2061: syntax error: identifier 'difference_type'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2051): error C2065: '_Alvbase': undeclared identifier
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2051): error C2923: 'std::_Rebind_alloc_t': '_Alvbase' is not a valid template type argument for parameter '_Alloc'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2058): error C2061: syntax error: identifier '_Sizet'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2065): error C2061: syntax error: identifier '_Sizet'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2072): error C2061: syntax error: identifier '_Sizet'
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2089): error C3646: '_Myoff': unknown override specifier
C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\VC\Tools\MSVC\14.16.27023\include\vector(2089): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

标签： c++visual-c++

解决方案

std::swap为as重载std::vector

template< class T, class Alloc>
void swap(vector<T,Alloc>& lhs, vector<T,Alloc>& rhs);

给定向量的正确模板参数是T=long, Alloc = std::allocator<long>. 在 an 上调用swap（或几乎任何其他模板化函数）的正确方法std::vector是完全删除显式模板参数规范并让模板参数推导完成其工作。

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