c++ - 如何在 vector 中找到一个项目？

Question

我有一段这样的代码。

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

using namespace std;

class A
{
    public:
        A(int iVal) : _val(iVal) {}
        int getVal() const { return _val; }
    private:
        int _val;
};

class B
{
    public:
        B(int iNum) : _num(iNum) {}
        int getNum() const { return _num; }
    private:
        int _num;
};

bool isInVecA(vector<A> vectorA, int iVal)
{
    for(vector<A>::const_iterator it=vectorA.begin(); it != vectorA.end(); it++)
    {
        if(it->getVal() == iVal)
            return true;
    }
    return false;
}

bool isInVecB(vector<B> vectorB, int iNum)
{
    for(vector<B>::const_iterator it=vectorB.begin(); it != vectorB.end(); it++)
    {
        if(it->getNum() == iNum)
            return true;
    }
    return false;
}

int main()
{    
    A arrayA[] = { A(1), A(2), A(3) };
    vector<A> vectorA(arrayA, arrayA + sizeof(arrayA) / sizeof(A));

    B arrayB[] = { B(3), B(4), B(5) };
    vector<B> vectorB(arrayB, arrayB + sizeof(arrayB) / sizeof(B));

    int key = 3;

    if(isInVecA(vectorA, key) && isInVecB(vectorB, key))
        cout << "Key " << key << " is in both vectors." << endl;
    else
        cout << "Key " << key << " is not in both vectors." << endl;

    return 0;
}

我想做的只是创建一些东西来替换函数 isInVecA 和 isInVecB 因为它们太相似了。假设我不能更改A类和B类。

---

非常感谢大家。我对 StackOverflow 很陌生。不知道在哪里发布我和我的 friend 想出的解决方案。因此，我把它放在这里。

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <functional>
#include <boost/bind.hpp>

using namespace std;

class A
{
    public:
        A(int iVal) : _val(iVal) {}
        int getVal() const { return _val; }
    private:
        int _val;
};

class B
{
    public:
        B(int iNum) : _num(iNum) {}
        int getNum() const { return _num; }
    private:
        int _num;
};

template<typename T>
bool isInVec(vector<T> vec, int (T::*func)() const, int iVal)
{
    return find_if(vec.begin(), vec.end(), boost::bind(func, _1) == iVal) != vec.end();
}

int main()
{    
    A arrayA[] = { A(1), A(2), A(3) };
    vector<A> vectorA(arrayA, arrayA + sizeof(arrayA) / sizeof(A));

    B arrayB[] = { B(3), B(4), B(5) };
    vector<B> vectorB(arrayB, arrayB + sizeof(arrayB) / sizeof(B));

    int key = 3;

    if(isInVec<A>(vectorA, &A::getVal, key) && isInVec<B>(vectorB, &B::getNum, key))
        cout << "Key " << key << " is in both vectors." << endl;
    else
        cout << "Key " << key << " is not in both vectors." << endl;

    return 0;
}

Answer 1

您可以创建比较器并使用 std::find_if .

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

using namespace std;

class A
{
    public:
        A(int iVal) : _val(iVal) {}
        int getVal() const { return _val; }
    private:
        int _val;
};

class B
{
    public:
        B(int iNum) : _num(iNum) {}
        int getNum() const { return _num; }
    private:
        int _num;
};

class cmpA
{
    private:
        int target;
    public:
        cmpA(int t) : target(t) {}
        bool operator()(const A& a) const {
            return a.getVal() == target;
        }
};
class cmpB
{
    private:
        int target;
    public:
        cmpB(int t) : target(t) {}
        bool operator()(const B& b) const {
            return b.getNum() == target;
        }
};

template<class T, class V>
bool isInVec(const vector<V>& vector, int iNum)
{
    return find_if(vector.begin(), vector.end(), T(iNum)) != vector.end();
}

int main(void) {
    A arrayA[] = { A(1), A(2), A(3) };
    vector<A> vectorA(arrayA, arrayA + sizeof(arrayA) / sizeof(A));

    B arrayB[] = { B(3), B(4), B(5) };
    vector<B> vectorB(arrayB, arrayB + sizeof(arrayB) / sizeof(B));

    int key = 3;

    if(isInVec<cmpA>(vectorA, key) && isInVec<cmpB>(vectorB, key))
        cout << "Key " << key << " is in both vectors." << endl;
    else
        cout << "Key " << key << " is not in both vectors." << endl;

    return 0;
}

更新:新代码，相似代码更少，基于Adapter Design Pattern的思想:

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

using namespace std;

class A
{
    public:
        A(int iVal) : _val(iVal) {}
        int getVal() const { return _val; }
    private:
        int _val;
};

class B
{
    public:
        B(int iNum) : _num(iNum) {}
        int getNum() const { return _num; }
    private:
        int _num;
};

// dummy number getter
template<class T> int getNumber(const T& x) { return 0; }

// number getter for class A
template<> int getNumber(const A& x) { return x.getVal(); }

// number getter for class B
template<> int getNumber(const B& x) { return x.getNum(); }

// comparator using the number getter
template<class T>
class cmp
{
    private:
        int target;
    public:
        cmp(int t) : target(t) {}
        bool operator()(const T& a) const { return getNumber<T>(a) == target; }
};

template<class T>
bool isInVec(const vector<T>& vector, int iNum)
{
    return find_if(vector.begin(), vector.end(), cmp<T>(iNum)) != vector.end();
}

int main(void) {
    A arrayA[] = { A(1), A(2), A(3) };
    vector<A> vectorA(arrayA, arrayA + sizeof(arrayA) / sizeof(A));

    B arrayB[] = { B(3), B(4), B(5) };
    vector<B> vectorB(arrayB, arrayB + sizeof(arrayB) / sizeof(B));

    int key = 3;

    if(isInVec(vectorA, key) && isInVec(vectorB, key))
        cout << "Key " << key << " is in both vectors." << endl;
    else
        cout << "Key " << key << " is not in both vectors." << endl;

    return 0;
}