当std::unordered_map被包装在类中时，它不接受std：：线程
当std::unordered_map被包装在类中时，它不接受std：：线程
提问于 2018-01-03 20:39:57
如果我试图将int和std::thread保存在std::unordered_map<int, std::thread>中，一切似乎都很好。
但是如果我包装了std::unordered_map，那么在标准库中就会出现一个错误。
错误是：no matching constructor for initialization of '_Mypair'
有什么方法可以绕过这个问题，让它在包装的时候工作吗？
这样做是可行的：
Source.cpp
#include <thread>
#include <unordered_map>
void display() {}
int main()
{
std::unordered_map<int, std::thread> map_;
std::thread tempThread(&display);
map_.emplace(0, std::move(tempThread));
return 0;
}这不管用：
MapperWrapper.h
#ifndef MAPPERWRAPPER_H
#define MAPPERWRAPPER_H
#include <unordered_map>
#include <utility>
template <typename KeyType, typename valueType> class MapperWrapper
{
public:
void add(KeyType key, valueType value)
{
mapper.emplace(std::make_pair(key, value));
}
protected:
std::unordered_map<KeyType, valueType> mapper;
};
#endif // MAPPERWRAPPER_HSource.cpp
#include <thread>
#include "MapperWrapper.h"
void display() {}
int main()
{
MapperWrapper<int, std::thread> map_;
std::thread tempThread(&display);
map_.add(0, std::move(tempThread));
return 0;
}这将生成错误：
||=== Build: Debug in Testing (compiler: LLVM Clang Compiler) ===|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|327|error: no matching constructor for initialization of '_Mypair' (aka 'pair<int, std::thread>')|
C:\Users\usr\Desktop\Project2\Project2\MapperWrapper.h|12|in instantiation of function template specialization 'std::make_pair<int &, std::thread &>' requested here|
C:\Users\usr\Desktop\Project2\Project2\Source.cpp|12|in instantiation of member function 'MapperWrapper<int, std::thread>::add' requested here|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|96|note: candidate template ignored: requirement 'is_copy_constructible<thread>::value' was not satisfied [with _Uty1 = int, _Uty2 = std::thread]|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|107|note: candidate template ignored: requirement 'is_copy_constructible<thread>::value' was not satisfied [with _Uty1 = int, _Uty2 = std::thread]|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|167|note: candidate template ignored: requirement 'is_constructible<thread, thread &>::value' was not satisfied [with _Other1 = int &, _Other2 = std::thread &]|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|181|note: candidate template ignored: requirement 'is_constructible<thread, thread &>::value' was not satisfied [with _Other1 = int &, _Other2 = std::thread &]|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|85|note: candidate constructor template not viable: requires 0 arguments, but 2 were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|121|note: candidate constructor template not viable: requires single argument '_Right', but 2 arguments were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|132|note: candidate constructor template not viable: requires single argument '_Right', but 2 arguments were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|150|note: candidate constructor template not viable: requires 4 arguments, but 2 were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|157|note: candidate constructor template not viable: requires 3 arguments, but 2 were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|195|note: candidate constructor template not viable: requires single argument '_Right', but 2 arguments were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|209|note: candidate constructor template not viable: requires single argument '_Right', but 2 arguments were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|112|note: candidate constructor not viable: requires 1 argument, but 2 were provided|
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility|113|note: candidate constructor not viable: requires 1 argument, but 2 were provided|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|回答 1
Stack Overflow用户
回答已采纳
发布于 2018-01-03 20:45:21
您已经接受了按值类型的值。因为函数参数是本地的，所以您可以移动它(也可以移动键)
void add(KeyType key, valueType value)
{
mapper.emplace(std::move(key), std::move(value));
}也没有必要使用std::make_pair将其嵌入到地图中。
如果您想变得更复杂一点，可以向add添加一些完善的转发支持，以避免创建多余的中间对象。
template<typename... Args>
void add(Args&&... args)
{
mapper.emplace(std::forward<Args>(args)...);
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/48084801
复制相关文章
相似问题
腾讯云开发者
