"Unidentified reference to '(function)'"错误

我有一个项目，有一个主文件（assign2.cpp），一个头文件（arithcard.hpp）和另一个名为arithcard.cpp文件的文件。

在头文件中，我定义了类和要使用的所有方法。在arithcard.cpp中，我将使用这些方法，在我的assign2.cpp文件中，我将调用它们。

当我构建项目时，它始终在我调用头文件中定义的方法时给出 4 个错误。

错误是：

"Unidentified reference to '(function)'"

我已经将头文件包含在.cpp两个文件中。
我正在使用Eclipse和minGW。有人可以在这里帮助我吗？

哦，是的！代码。对不起，这么多评论。这是因为这是一项任务。

分配2.cpp

#include <iostream>
#include <sstream>
#include <string>
#include <limits>
#include <random>
#include "arithcard.hpp"
// File-local anonymous namespace
namespace {
int verbosity = 1 ;
}
/*
  Read in the files of cards, then loop: query the user to specify a
  question, print the question, check the answer. Terminate when the user
  types an empty line instead of specifying a question.
*/
int main (int argc, const char *argv[])
{
  if (argc != 2) {
    std::cout << "Usage: " << argv[0] << " <datafile>" << std::endl ;
    return (1) ;
  }
  std::string dataFile(argv[1]) ;
  bool result = false ;
  int cardCnt = -1 ;
  ArithCard *cards = nullptr ;
/*
  Parse the file of questions & answers. A false return value indicates an
  absent file or other i/o error. It's also possible the file is present but
  contains no valid questions.
*/
  result = ArithCard::readCards(dataFile,cardCnt,cards);
  if (!result) {
    if (verbosity >= 1) {
      std::cout
    << "Cannot locate file with questions; exiting." << std::endl ;
    }
    return (1) ;
  }
  if (cardCnt == 0) {
    if (verbosity >= 1) {
      std::cout << "Card file was empty, exiting." << std::endl ;
    }
    return (1) ;
  }
/*
  Create a random number generator and distribution to use below.
*/
  std::minstd_rand generator ;
  std::uniform_int_distribution<int> randNum(1,cardCnt) ;
/*
  Set up to ask the user to specify questions and start a loop. Note
  that an empty line is the only way to end this loop. Given the context
  (valid user input is small integers), go with a fixed maximum line size.
*/
  const int MAXLINE = 120 ;
  char inBuf[MAXLINE] ;
  do {
/*
  Prompt the user to select a question. Exit on an empty line. Use getline
  because stream i/o with '>>' will eat empty lines and never return.
*/
    std::cout
      << "Enter a number between 1 and " << cardCnt
      << " (0 for random, enter to quit): " ;
    std::cin.getline(inBuf,MAXLINE) ;
    if (inBuf[0] == '') {
      std::cout << "Exiting." << std::endl ;
      break ;
    }
/*
  Make sure the answer is a valid integer, and nothing but a valid integer. If
  the user specifies `0', pick a card at random.
*/
    std::istringstream parseStream(inBuf) ;
    int userNumber = -1 ;
    parseStream >> userNumber ;
    if (parseStream.fail()) {
      std::cout
    << "The string '" << inBuf << "' is not a valid number."
    << std::endl ;
      continue ;
    }
    if (!parseStream.eof()) {
      std::cout
        << "The string '" << inBuf << "' contains more than an integer."
    << std::endl ;
      continue ;
    }
    if (userNumber < 0 || userNumber > cardCnt) {
      std::cout
        << "The number " << userNumber << " is out of range." << std::endl ;
      continue ;
    }
    if (userNumber == 0) {
      userNumber = randNum(generator) ;
    }
    userNumber-- ;
/*
  Display the question, then read and check the user's answer.
*/
    cards[userNumber].displayQuestion(std::cout) ;
    result = cards[userNumber].checkAnswer(std::cin) ;
    if (result == true) {
      std::cout << "Correct!" << std::endl ;
    } else {
      std::cout
        << "Incorrect; the correct answer is "
    << cards[userNumber].getAnswer() << std::endl ;
    }
  } while (true) ;
/*
  Done! Delete the card array and return.
*/
  delete[] cards ;
  return (0) ;
}

算术卡.hpp

#include <iostream>
#include <string>
/*
  Defines the class ArithCard, for handling arithmetic flash cards.
  You may not modify the public method declarations provided below. The main
  program used to test your solution will assume that these methods exist.
  You can add private attributes and methods as you need them.
  You may find it convenient to add additional public methods for testing.
  Keep in mind that your code must work with the unmodified main program
  or it will fail automated testing.
*/
class ArithCard {
  public:
  // Default constructor
  ArithCard() ;
  /*
    Read arithmetic questions and answers from the specified file and
    construct an array of ArithCard objects. A pointer to the array is
    returned in cards. The number of ArithCard objects in the array is
    returned in cardCnt.
    If the file cannot be opened, the method returns false, otherwise it
    returns true.
    If there are no valid questions in the file, cardCnt is set to zero. If
    cardCnt is zero, the value of cards is undefined and should not be used.
    Calling readCards with cardCnt = 0 and cards == nullptr is the expected
    way to use this method.
  */
  static bool readCards(const std::string &fileName,
            int &cardCnt, ArithCard *&cards) ;
  /*
    Write the question to the specified output stream.
  */
  void displayQuestion(std::ostream &out) ;
  /*
    Read the user's answer from the specified input stream and compare it with
    the correct answer.
    Returns true if the answer is correct, false otherwise.
  */
  bool checkAnswer(std::istream &in) ;
  // Return the question as a string.
  std::string getQuestion() ;
  // Return the answer as a string.
  std::string getAnswer() ;
  // Return the answer as an integer.
  int getAnswerValue() ;
  private:
  // Add your private methods and attributes here.
  std::string question;
  int answer;
} ;

算术卡.cpp

#include <iostream>
#include <string>
#include "arithcard.hpp"
#include <sstream>
bool readCards(const std::string &fileName, int &cardCnt, ArithCard *&cards)
{
    return (true);
}
void displayQuestion(std::ostream &out)
{
}
bool checkAnswer(std::istream &in)
{
    return (false);
}
std::string getQuestion()
{
    return("question");
}
std::string getAnswer()
{
    return ("answerswer");
}
int getAnswerValue()
{
    return 1;
}