16

我对 c++ 很陌生，我正在尝试找到一种方法来搜索结构向量以查找具有特定成员数据的结构。

我知道这适用于向量中的简单类型

std::find(vector.begin(), vector.end(), item) != vector.end()

但是可以说我有一个这样的结构：

struct Friend
{
  string name;
  string number;
  string ID;
};

和这样的向量：

vector<Friend> friends;

然后向量充满了朋友。

假设我想搜索具有某个 ID 的朋友，并找出详细信息。或者从向量中删除某个结构。有没有一种简单的方法可以做到这一点？

4

4 回答 4

25

This can be done with std::find_if and a search predicate, which can be expressed as a lambda function if you have C++11 (or C++0x) available:

auto pred = [](const Friend & item) {
    return item.ID == 42;
};
std::find_if(std::begin(friends), std::end(friends), pred) != std::end(friends);

To use an ID given as a variable, you have to capture it in the lambda expression (within the [...]):

auto pred = [id](const Friend & item) {
    return item.ID == id;
};
std::find_if(std::begin(friends), std::end(friends), pred) != std::end(friends);

If you don't have C++11 available, you have to define the predicate as a functor (function object). Remy Lebeau's answer uses this approach.

To remove elements matching the criteria as defined by the predicate, use remove_if instead of find_if (the rest of the syntax is the same).

For more algorithms, see the STL <algorithm> reference.

于 2013-01-08T23:39:19.047 回答
13

Use std::find_if(). @leemes and @AndyProwl showed you how to use it in a C++11 compiler. But if you are not using a C++11 compiler, then you can use it like this instead, which defines a functor comparing the ID of a given item with a previously specified ID in its constructor:

class MatchesID
{
    std::string _ID;

public:
    MatchesID(const std::string &ID) : _ID(ID) {}

    bool operator()(const Friend &item) const
    {
        return item.ID == _ID;
    }
};

std::find_if(vector.begin(), vector.end(), MatchesID("TheIDHere")) != vector.end();

If you have other classes in your project which use IDs, you can make this functor templated:

template<typename IDType>
class MatchesID
{
    IDType _ID;

public:
    MatchesID(const IDType &ID) : _ID(ID) {}

    template<class ItemType>
    bool operator()(const ItemType &item) const
    {
        return item.ID == _ID;
    }
};

std::find_if(vector.begin(), vector.end(), MatchesID<std::string>("TheIDHere")) != vector.end();
于 2013-01-08T23:43:37.257 回答
4

You can use std::find_if in combination with functors (if you are working with C++98) or lambdas (if you are using C++11, which I will assume):

using namespace std;
int ID = 3; // Let's say...
auto it = find_if(begin(vector), end(vector), [=] (Friend const& f) { 
    return (f.ID == ID); 
    });
bool found = (it != end(vector));
于 2013-01-08T23:40:59.820 回答
2

If you want to find an element in STL container, use std::find or std::find_if algorithms With C++03, you need to overload operator== for std::find

bool operator==(const Friend& lhs, const Friend& rhs)
{
  return lhs.ID == rhs.ID;
}

if (std::find(friends.begin(), friends.end(), item) != friends.end())
{
   // find your friend
}

OR C++11 with lambda:

std::find_if(friends.begin(), friends.end(),  [](Friend& f){ return f.ID == "1"; } );

If you want to remove a certain element, use std::remove_if

std::remove_if(friends.begin(), friends.end(), 
      [](Friend& f){ return f.ID == "1"; });
于 2013-01-08T23:45:46.507 回答