使用STL查找向量中的所有元素 [英] using STL to find all elements in a vector

问题描述

我有一个元素集合，我需要操作，调用成员函数上的集合：

I have a collection of elements that I need to operate over, calling member functions on the collection:

std::vector<MyType> v;
... // vector is populated

-forward：

std::for_each(v.begin(), v.end(), std::mem_fun(&MyType::myfunc));

如果要调用的函数有一个参数，也可以这样做。

A similar thing can be done if there's one argument to the function I wish to call.

我的问题是，如果它满足一些条件，我想在向量中的元素上调用一个函数。 std :: find_if 返回一个迭代器到满足谓词条件的第一个元素。

My problem is that I want to call a function on elements in the vector if it meets some condition. std::find_if returns an iterator to the first element meeting the conditions of the predicate.

std::vector<MyType>::iterator it  = 
      std::find_if(v.begin(), v.end(), MyPred());

我希望找到符合谓词的所有元素并对它们进行操作。

I wish to find all elements meeting the predicate and operate over them.

我一直在寻找 find_all 或 do_if 等价，或者我可以用现有的STL（这样我只需要迭代一次），而不是滚动我自己或简单做一个标准的迭代使用for循环和比较。

I've been looking at the STL algorithms for a "find_all" or "do_if" equivalent, or a way I can do this with the existing STL (such that I only need to iterate once), rather than rolling my own or simply do a standard iteration using a for loop and comparisons.

推荐答案

Boost Lambda让这很容易。

Boost Lambda makes this easy.

#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>
#include <boost/lambda/if.hpp>

std::for_each( v.begin(), v.end(), 
               if_( MyPred() )[ std::mem_fun(&MyType::myfunc) ] 
             );

如果它很简单，你甚至可以省略定义MyPred这是lambda真正发光的地方。例如，如果MyPred意思是可被2整除：

You could even do away with defining MyPred(), if it is simple. This is where lambda really shines. E.g., if MyPred meant "is divisible by 2":

std::for_each( v.begin(), v.end(), 
               if_( _1 % 2 == 0 )[ std::mem_fun( &MyType::myfunc ) ]
             );

---

更新：
使用C ++ 0x lambda语法也是非常好的（继续使用谓词模2）：

---

Update: Doing this with the C++0x lambda syntax is also very nice (continuing with the predicate as modulo 2):

std::for_each( v.begin(), v.end(),
               [](MyType& mt ) mutable
               {
                 if( mt % 2 == 0)
                 { 
                   mt.myfunc(); 
                 }
               } );

乍一看，这看起来像是从boost :: lambda语法向后退一步，因为更复杂的函子逻辑很容易实现与c ++ 0x语法...其中任何非常复杂的boost :: lambda很快就很棘手。 Microsoft Visual Studio 2010 beta 2目前实现此功能。

At first glance this looks like a step backwards from boost::lambda syntax, however, it is better because more complex functor logic is trivial to implement with c++0x syntax... where anything very complicated in boost::lambda gets tricky quickly. Microsoft Visual Studio 2010 beta 2 currently implements this functionality.

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