Question

以下表达式对for_each()有效吗？

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

参考：CppCoreGuidelines.md#p3-express-intent

上面的表达式抛出错误：

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

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

如果它们实际上是指std::for_each，那么它将是一个拼写错误，因为它需要两个迭代器 - 除非它们指的是std::for_each that might be introduced with the Ranges proposals的未来版本。

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);
}

C ++表达式for_each（v，[]（字符串x）在语法上是否正确？

1 个答案: