是std::async
可以使用模板函數嗎?我試圖將std::reverse
作爲一個異步任務BU得到編譯時錯誤。std :: async可以與模板函數一起使用
我試過使用更簡單的函數(foo和bar),並發現只有非模板函數正在工作。
#include <algorithm>
#include <future>
#include <string>
void foo(std::string::iterator first, std::string::iterator last)
{
}
template<class BidirectionalIterator>
void bar(BidirectionalIterator first, BidirectionalIterator last)
{
}
int main()
{
std::string str = "Lorem ipsum, dolor sit amet";
auto result_reverse = std::async(std::reverse, str.begin(), str.end()); // Compile-time error
auto result_foo = std::async(foo, str.begin(), str.end());
auto result_bar = std::async(bar, str.begin(), str.end()); // Compile-time error
result_reverse.get();
result_foo.get();
result_bar.get();
}
編譯器錯誤是如下:
main.cpp: In function ‘int main()’:
main.cpp:18:71: erreur: no matching function for call to ‘async(<unresolved overloaded function type>, std::basic_string<char>::iterator, std::basic_string<char>::iterator)’
main.cpp:18:71: note: candidates are:
/usr/include/c++/4.6/future:1355:5: note: template<class _Fn, class ... _Args> std::future<typename std::result_of<_Functor(_ArgTypes ...)>::type> std::async(std::launch, _Fn&&, _Args&& ...)
/usr/include/c++/4.6/future:1378:5: note: template<class _Fn, class ... _Args> typename std::__async_sfinae_helper<typename std::decay<_Functor>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...)
main.cpp:18:71: erreur: unable to deduce ‘auto’ from ‘<expression error>’
main.cpp:20:62: erreur: no matching function for call to ‘async(<unresolved overloaded function type>, std::basic_string<char>::iterator, std::basic_string<char>::iterator)’
main.cpp:20:62: note: candidates are:
/usr/include/c++/4.6/future:1355:5: note: template<class _Fn, class ... _Args> std::future<typename std::result_of<_Functor(_ArgTypes ...)>::type> std::async(std::launch, _Fn&&, _Args&& ...)
/usr/include/c++/4.6/future:1378:5: note: template<class _Fn, class ... _Args> typename std::__async_sfinae_helper<typename std::decay<_Functor>::type, _Fn, _Args ...>::type std::async(_Fn&&, _Args&& ...)
main.cpp:20:62: erreur: unable to deduce ‘auto’ from ‘<expression error>’
然而,它傳遞的時候我手動指定模板instanciation,如std::async(std::reverse<std::string::iterator>, str.begin(), str.end())
。
這是一個編譯器錯誤(GCC 4.6.3)還是定義良好的行爲?
模板是沒有的功能,所以其行爲依據的標準是正確的。如果你想推導出參數,你需要將它包裝在仿函數中。 – Xeo