Trouble overloading extraction operator for custom PriorityQueue - c++

Question

I am trying to overload operator>> for a custom PriorityQueue class I've been writing, code is below:
/**
* #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;
}
This currently works for stdin or std::cin input however it doesn't work for fstream input - the very first getline always reads an empty line from the input such that the while loop never gets triggered, and I can't seem to skip it (I tried with inStream.ignore() as you can see above but this doesn't work.
Edit:
Currently I just want to get it working for file input ignoring the fact it only works for int data type and double priority type right now - these aren't relevant (and neither is the actual manipulation of the targetQueue object itself).
For the moment I'm just concerned with resolving the blank-line issue when trying to stream through file-input.
Example file to pass:
3 5.6
2 6.3
1 56.7
12 45.1
where the numbers on each line are \t separated.
Example testing:
#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;
}
where "test.txt" is the in the format of the example file above.
Edit: Simpler Example
Code:
#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

The operator is already overloaded -- and shall be overloaded -- for many types. Let those functions do their work:
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;
}