向std :: vector或typdef添加自定义方法 [英] Adding custom methods to std::vector or typdef

问题描述

因此，我有以下代码，可以搜索一个向量中的对象的字符串。

  #include< iostream> 
 #include< fstream> 
 #include< vector> 
 #include< algorithm> 
 #include< string> 
 
 struct migObj 
 {
 migObj（const std :: string& a_name，const std :: string& a_location）：name（a_name），location（a_location）{} 
 std :: string name; 
 std :: string location; 
}; 
 
 int main（）
 {
 typedef std :: vector< migObj> migVec; 
 migVec v; 
 v.push_back（migObj（fred，belfast））; 
 v.push_back（migObj（ivor，london））; 
 
 //按名称搜索。 
 const std :: string name_to_find =ivor; 
 auto i = std :: find_if（v.begin（），v.end（），[&]（const migObj& obj）{return name_to_find == obj.name;}）; 
 if（i！= v.end（））
 {
 std :: cout< i-> name<< ，< i->位置<< \\\
; 
} 
 
 return 0; 
} 
  

commecntname by name下面的代码负责此结果。我想做的是做一个方法添加到std :: vector或者typedef migVec，所以我可以调用

解决方案

你不能这样做：C ++不有与C＃中类似的扩展方法。

您可以从向量派生类，但是必须更改所有客户端代码。此外，正如Roddy指出的，std :: vector没有虚拟析构函数，所以从中推导出来是一个不好的想法。

函数会是更好的选择。额外的好处是，它也适用于大多数其他容器（例如 std :: list ），并且更加兼容STL中的大多数算法，这些算法通常也是自由功能。 / p>

所以你会有这样的：

  myNewSearchFunction（v， ivor）; // instead of v.myNewSearchFunction（ivor）; 
  

在内部，此函数 std :: find_if（v.begin ，v.end（），... 。

BTW，请注意，最好使用 std :: begin（v），std :: end（v）比 v.begin（），v.end（）您可以在数组上运行相同的代码。

将事物放入类中并不总是在C ++中的最佳选择。

So I have the following code that makes it possible to "search" for a string of an object in a vector.

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <string>

struct migObj
{
    migObj(const std::string& a_name, const std::string& a_location) : name(a_name),             location(a_location) {}
    std::string name;
    std::string location;
};

int main()
{
    typedef std::vector<migObj> migVec;
    migVec v;
    v.push_back(migObj("fred", "belfast"));
    v.push_back(migObj("ivor", "london"));

    // Search by name.
    const std::string name_to_find = "ivor";
    auto i = std::find_if(v.begin(), v.end(), [&](const migObj& obj) { return name_to_find == obj.name;});
    if (i != v.end())
    {
        std::cout << i->name << ", " << i->location << "\n";
    }

    return 0;
}

The code below the commecnt "search by name" is responsible for this result. What I want to do is make a method that is either added to the std::vector or to the typedef migVec, so I can call

v.myNewSearchFunction("ivor");

解决方案

You can't do that: C++ doesn't have extension methods similar to what you have in C#.

You could derive your class from vector, but then you have to change all the client code. Besides, as Roddy points out, std::vector doesn't have a virtual destructor, so deriving from it is a bad idea in general.

IMO, writing a simple function would be much better choice. Additional benefit is that it would also work for most other containers (e.g. std::list) and be more compatible with most of algorithms in STL which are also typically free functions.

So you would have this instead:

myNewSearchFunction(v, "ivor"); // instead of v.myNewSearchFunction("ivor");

Internally, this function does std::find_if(v.begin(), v.end(), ....

BTW, please note that it would be better to use std::begin(v), std::end(v) than v.begin(), v.end(). This lets you run the same code on e.g. arrays.

Putting things into classes isn't always the best choice in C++.

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