template<typename T>
auto do_something(T input) {
  std::this_thread::sleep_for(std::chrono::seconds(1));
  return 123;
}

int main(int argc,char *argv[]) {
  std::function<int(void)> function = std::bind(do_something<int>,12);
  function();
  return 0;
}

使用GCC 6.1.1,我收到此错误：

test.cpp: In function ‘int main(int,char**)’:
test.cpp:16:70: error: no matching function for call to ‘bind(<unresolved overloaded function type>,int)’
   std::function<int(void)> function = std::bind(do_something<int>,12);
                                                                      ^
In file included from /usr/include/c++/6.1.1/thread:39:0,from test.cpp:4:
/usr/include/c++/6.1.1/functional:1331:5: note: candidate: template<class _Func,class ... _BoundArgs> typename std::_Bind_helper<std::__is_socketlike<_Func>::value,_Func,_BoundArgs ...>::type std::bind(_Func&&,_BoundArgs&& ...)
     bind(_Func&& __f,_BoundArgs&&... __args)
     ^~~~
/usr/include/c++/6.1.1/functional:1331:5: note:   template argument deduction/substitution Failed:
test.cpp:16:70: note:   couldn't deduce template parameter ‘_Func’
   std::function<int(void)> function = std::bind(do_something<int>,from test.cpp:4:
/usr/include/c++/6.1.1/functional:1359:5: note: candidate: template<class _Result,class _Func,class ... _BoundArgs> typename std::_Bindres_helper<_Result,_BoundArgs>::type std::bind(_Func&&,_BoundArgs&&... __args)
     ^~~~
/usr/include/c++/6.1.1/functional:1359:5: note:   template argument deduction/substitution Failed:
test.cpp:16:70: note:   couldn't deduce template parameter ‘_Result’
   std::function<int(void)> function = std::bind(do_something<int>,12);

如您所见,编译器无法推断出函数的结果类型.

注意：clang 3.8.0可以编译,没有任何错误.

所以我的问题是：有没有办法在这种情况下指定模板函数的预期返回值？

解决方法

#include <functional>

template<typename T>
auto do_something(T input) {
  return 123;
}

// Make the compiler workout the type of do_something<int> so we can use it later.
auto f = do_something<int>;

int main(int argc,12);
  function();
  return 0;
}

• 上一篇：C中的按位移位问题下一篇：将不同的C标准与GCC混合