如何从 c++ 中的模板 class 调用 function

Question

这个模板 function 对我来说是新的，因为我正在学习。 我需要将比较从 BinarySearch() 传递给 Comparer() 以显示比较执行了多少元素。 如何在 BinarySearch() 中调用 Comparer()？ 这是为了查找字符串是否在数组中。

#ifndef INTCOMPARER_H
#define INTCOMPARER_H

#include "Comparer.h"

class IntComparer : public Comparer<int> {
public:
    int Compare(const int& a, const int& b) override {
        if (a < b) {
            return -1;
        }
        else if (a > b) {
            return 1;
        }
        return 0;
    }
};
#endif

#ifndef COMPARER_H
#define COMPARER_H

template <typename T>
class Comparer {
public:
    virtual int Compare(const T& a, const T& b) = 0;
};

#endif

#ifndef SEARCHER_H
#define SEARCHER_H

#include "Comparer.h"

template <typename T>
class Searcher {
public:
    // I need to call the Comparer() inside this BinarySearch().
    static int BinarySearch(T* array, int arraySize, const T& key,
        Comparer<T>& comparer) 
    {
        int low = 0;
        int high = arraySize - 1;
        int mid = 0;
        int test;
      
        while (high >= low) {
            mid = (high + low) / 2;
            if (array[mid] < key) {
                low = mid + 1;               
            }
            else if (array[mid] > key) {
                high = mid - 1;                
            }
            else
            {
                return mid;
            }
            return array.template Comparer<int>(1, 2);
        }
        return -1;
    }
};
#endif

Answer 1

BinarySearch()接受对实现Comparer<T>的 object 的引用。 它可以在需要时调用该 object 上的Compare()方法，例如：

#ifndef SEARCHER_H
#define SEARCHER_H

#include "Comparer.h"

template <typename T>
class Searcher {
public:
    static int BinarySearch(T* array, int arraySize, const T& key,
        Comparer<T>& comparer) 
    {
        int low = 0;
        int high = arraySize - 1;
        int mid = 0;
        int test;
      
        while (high >= low) {
            mid = (high + low) / 2;
            test = comparer.Compare(array[mid], key); // <-- here
            if (test < 0) {
                low = mid + 1;               
            }
            else if (test > 0) {
                high = mid - 1;                
            }
            else {
                return mid;
            }
        }
        return -1;
    }
};

#include "searcher.h"
#include "intcomparer.h"

int main() {
    int arr[5] = {1, 2, 3, 4, 5};
    int key = ...;
    IntComparer comp;

    cout << "found at " << Searcher<int>::BinarySearch(arr, 5, key, comp);
}