自定義PriorityQueue的問題重載提取運算符

Question

我正在嘗試為我一直在編寫的自定義PriorityQueue類重載operator>> ，代碼如下：

/**
 * @brief Overloaded stream extraction operator.
 *
 * Bitshift operator>>, i.e. extraction operator. Used to write data from an input stream
 * into a targeted priority queue instance. The data is written into the queue in the format,
 *
 * \verbatim
 [item1] + "\t" + [priority1] + "\n"
 [item2] + "\t" + [priority2] + "\n"
 ...
 * \endverbatim
 *
 * @todo Implement functionality for any generic Type and PriorityType.
 * @warning Only works for primitives as template types currently!
 * @param inStream Reference to input stream
 * @param targetQueue Instance of priority queue to manipulate with extraction stream
 * @return Reference to input stream containing target queue data
 */
template<typename Type, typename PriorityType> std::istream& operator>>(std::istream& inStream, PriorityQueue<Type, PriorityType>& targetQueue) {

    // vector container for input storage
    std::vector< std::pair<Type, PriorityType> > pairVec;
    // cache to store line input from stream
    std::string input;

    std::getline(inStream, input);

    if (typeid(inStream) == typeid(std::ifstream)) {
        inStream.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    }

    // loop until empty line
    while (!input.empty()) {
        unsigned int first = 0;
        // loop over input cache
        for (unsigned int i = 0; i < input.size(); ++i) {
            // if char at index i of cache is a tab, break from loop
            if (input.at(i) == '\t')
                break;
            ++first;
        }
        std::string data_str = input.substr(0, first);
        // convert from std::string to reqd Type
        Type data = atoi(data_str.c_str());

        std::string priority_str = input.substr(first);
        // convert from std::string to reqd PriorityType
        PriorityType priority = atof(priority_str.c_str());

        pairVec.push_back(std::make_pair(data, priority));

        // get line from input stream and store in input string
        std::getline(inStream, input);
    }

    // enqueue pairVec container into targetQueue
    //targetQueue.enqueueWithPriority(pairVec);

    return inStream;

}

目前，該方法適用於stdin或std::cin輸入，但不適用於fstream輸入-第一條getline始終從輸入中讀取空行，以使while循環永遠不會觸發，而且我似乎無法跳過它（我在inStream.ignore()嘗試過，如您在上面看到的那樣，但這不起作用。

編輯：

目前，我只是想讓它適用於文件輸入，而忽略了它現在僅適用於int數據類型和double優先級類型的事實-這些都不相關（與targetQueue對象本身的實際操作也不相關）。

目前，我只想解決嘗試通過文件輸入流式傳輸時出現的空白行問題。

要傳遞的示例文件：

3    5.6
2    6.3
1    56.7
12   45.1

每行數字之間用\\t分隔。

測試示例：

#include "PriorityQueue.h"
#include <sstream>
#include <iostream>
#include <fstream>

int main(void) {

    // create pq of MAX binary heap type
    PriorityQueue<int, double> pq(MAX);


    std::ifstream file("test.txt");

    file >> pq;

    std::cout << pq;

}

其中“ test.txt”是上面示例文件的格式。

編輯：更簡單的例子

碼：

#include <iostream>
#include <fstream>
#include <vector>

class Example {

public:

    Example() {}

    size_t getSize() const { return vec.size(); }

    friend std::istream& operator>>(std::istream& is, Example& example);

private:

    std::vector< std::pair<int, double> > vec;

};

std::istream& operator>>(std::istream& is, Example& example) {

    int x;
    double y;
    while (is >> x >> y) {
        std::cout << "in-loop" << std::endl;
        example.vec.push_back(std::make_pair(x, y));
    }
    return is;
}

int main(void) {

    Example example;

    std::ifstream file("test.txt");

    file >> example;

    file.close();

    std::cout << example.getSize() << std::endl;

    return 0;

}

Answer 1

對於許多類型，運算符已經超載-並且應該超載。 讓這些功能發揮作用：

template<typename Type, typename PriorityType>
std::istream& operator>>(std::istream& inStream, PriorityQueue<Type, PriorityType>& targetQueue)
{
  std::vector< std::pair<Type, PriorityType> > pairVec;
  Type data;
  PriorityType priority;

  while(inStream >> data >> priority)
    pairVec.push_back(std::make_pair(data, priority));

  targetQueue.enqueueWithPriority(pairVec);

  return inStream;
}