c++ - C++ 表达式 for_each(v, [](string x) 在语法上是否正确？

Question

下面的表达式对 for_each() 有效吗？

for_each(v,[](string x){
    cout<<x<<endl;
});

引用:CppCoreGuidelines.md#p3-express-intent

上面的表达式抛出以下错误:

error: no matching function for call to ‘for_each(std::vector<std::__cxx11::basic_string<char> >&,
main()::<lambda(std::__cxx11::string)>)’
     });
      ^
In file included from /usr/include/c++/5/algorithm:62:0,
                 from test.cpp:4:
/usr/include/c++/5/bits/stl_algo.h:3761:5: note: candidate: template<class _IIter, class _Funct> _Funct std::for_each(_IIter,
_IIter, _Funct)
     for_each(_InputIterator __first, _InputIterator __last, _Function __f)
     ^
/usr/include/c++/5/bits/stl_algo.h:3761:5: note:   template argument deduction/substitution failed:
test.cpp:60:6: note:   deduced conflicting types for parameter ‘_IIter’ (‘std::vector<std::__cxx11::basic_string<char> >’ and
‘main()::<lambda(std::__cxx11::string)>’)
     });

Answer 1

好吧，核心指南提到了 for_each，而不是 std::for_each。所以很难回答你的问题...

• 如果他们实际上指的是 std::for_each，那么这将是一个打字错误，因为它需要两个迭代器 - 除非他们指的是 future 版本的 std::for_each that might be introduced with the Ranges proposals .

• 如果他们指的是通用for_each，那么它可能只是:

  template <typename TContainer, typename TF>
  void for_each(TContainer&& c, TF&& f)
  {
      for(auto&& x : c) f(x);
  }