c ++：覆蓋運算符時的多個定義

Question

我正在為一個有理數的類實現一個類，當然這涉及到覆蓋'=='和'！='等常用運算符。 我很確定在某個地方有一個我丟失的愚蠢錯誤，請不要猶豫，要求我提供任何我沒有提供的文件。 謝謝！

rational.hpp：

#ifndef RATIONAL_HPP
#define RATIONAL_HPP

#include "test.hpp"

#include <cstdlib>
#include <iosfwd>
#include <iostream>
#include <assert.h>

// Mathematical helper functions.
//
// NOTE: These are defined in rational.cpp.
int gcd(int, int);
int lcm(int, int);


// Represents a rational number. The rational numbers are the set of
// numbers that can be represented as the quotient of two integers.
struct Rational
{
  // TODO: Define the following:
  // 1. A default constructor
    int n;
    int d;
    Rational()
    :n(0), d(1) {}

  // 2. A constructor that takes an integer value
    Rational(int num)
    :n(num), d(1){}
  // 3. A constructor that takes a pair of values
    Rational(int numer, int denom)
    :n(numer), d(denom) {
    assert( d != 0);
        int gcdnum;
        if ((numer % denom) != 0){
            //do nothing
        }else{
            gcdnum = gcd(numer, denom);
            numer /= gcdnum;
            denom /= gcdnum;
            Rational(numer, denom);
        }
    }
  // Returns the numerator.
  int num() const { 
    return n;
}

  // Returns the denominator
  int den() const { 
    return d;
 }

};


bool operator==(Rational a, Rational b){
        return (a.n == b.n && a.d == b.d);
}
bool operator!=(Rational a, Rational b){
        return (a.n != b.n && a.d != b.d);
}
bool operator < (Rational a, Rational b){
        int lcdNum = lcm(a.d, b.d);
        int newAN, newBN; //allows for comparisons without altering actuial value
        newAN = a.n * lcdNum;
        newBN = b.n * lcdNum;
        return newAN < newBN;
}
bool operator > (Rational a, Rational b){
        int lcdNum = lcm(a.d, b.d);
        int newAN, newBN; //allows for comparisons without altering actuial value
        newAN = a.n * lcdNum;
        newBN = b.n * lcdNum;
        return newAN > newBN;
}
bool operator <= (Rational a, Rational b){
        int lcdNum = lcm(a.d, b.d);
        int newAN, newBN; //allows for comparisons without altering actuial value
        newAN = a.n * lcdNum;
        newBN = b.n * lcdNum;
        return newAN <=  newBN;
}

bool operator >= (Rational a, Rational b){
        int lcdNum = lcm(a.d, b.d);
        int newAN, newBN; //allows for comparisons without altering actuial value
        newAN = a.n * lcdNum;
        newBN = b.n * lcdNum;
        return newAN >= newBN;
}

// 3. The standard arithmetic operators
//    - r1 + r2
//    - r1 - r2
//    - r1 * r2
//    - r1 / r2
//    - r1 / r2
Rational operator + (Rational a, Rational b){
    int lcdNum = lcm(a.d, b.d);
    int newAN, newBN; //allows for comparisons without altering actuial value
    newAN = a.n * lcdNum;
    newBN = b.n * lcdNum;
    Rational c((newAN + newBN), (a.d * lcdNum));
    return c;
}
Rational operator - (Rational a, Rational b){
    int lcdNum = lcm(a.d, b.d);
    int newAN, newBN; //allows for comparisons without altering actuial value
    newAN = a.n * lcdNum;
    newBN = b.n * lcdNum;
    Rational c((newAN + newBN), (a.d * lcdNum));
    return c;
}
Rational operator * (Rational a, Rational b){
    Rational c((a.n * b.n), (a.d * b.d));
    return c;
}
Rational operator / (Rational a, Rational b){
    Rational c((a.n * b.d), (a.d * b.n)); //multiplies by the reciprocal
    return c;
}


std::ostream& operator<<(std::ostream&, Rational);
std::istream& operator>>(std::istream&, Rational&);


#endif

rational.cpp：

//
// rational.hpp: Definition of rational class and its interace.

#include "rational.hpp"

#include <iostream>


// -------------------------------------------------------------------------- //
// Helper functions

// Compute the GCD of two integer values using Euclid's algorithm.
int
gcd(int a, int b)
{
  while (b != 0) {
    int t = b;
    b = a % b;
    a = t;
  }
  return a;
}


// Compute the LCM of two integer values.
int
lcm(int a, int b)
{
  return (std::abs(a) / gcd(a, b)) * std::abs(b);
}


// -------------------------------------------------------------------------- //
// Rational implementation


// TODO: Make this print integers when the denominator is 1.
 std::ostream&
 operator<<(std::ostream& os, Rational r)
{
  if(r.den() == 1){
   return os << r.num();
}else{
  return os << r.num() << '/' << r.den();
}
}


// TODO: Make this read integer values if no '/' is given as a separator.
// You may assume that there is no space between the numerator and the
// slash. Hint, find and read the reference documentation for istream::peek().
 std::istream&
 operator>>(std::istream& is, Rational& r)
{
  int p, q;
  char c;
  is >> p;
  c = is.peek();
  if (c == '/'){
    is >> c >> q;
    if (!is)
      return is;

     // Require that the divider to be a '/'.
    if (c != '/') {
      is.setstate(std::ios::failbit);
      return is;
    }

    // Make sure that we didn't read p/0.
    if (q == 0) {
      is.setstate(std::ios::failbit);
      return is;
    }

    r = Rational(p, q);
    return is;
  }else{
    is.setstate(std::ios::failbit);
}
}

rc.cpp：

// main.cpp: rational number test suite

#include "rational.hpp"

#include <iostream>
#include <iomanip>

#include <unistd.h>


int
main()
{
  // Determine if input is coming from a terminal.
  bool term = isatty(0);

  // This will continue reading until it reaches the end-of-input.
  // If you are using this interactivly, type crtl-d to send the
  // end of input character to the terminal.
  while (std::cin) {
    Rational r1;
    Rational r2;
    std::string op;

    if (term)
      std::cout << "> ";

    std::cin >> r1 >> op >> r2;
    if (!std::cin)
      break;

    // FIXME: Add all of the other overlaoded operators by adding
    // cases for each of them.
    if (op == "==") 


     std::cout << std::boolalpha << (r1 == r2) << '\n';
    else if (op == "!=")
     std::cout << std::boolalpha << (r1 != r2) << '\n';
    else if (op == "<")
     std::cout << std::boolalpha << (r1 < r2) << '\n';
    else if (op == ">")
     std::cout << std::boolalpha << (r1 > r2) << '\n';
    else if (op == "<=")
     std::cout << std::boolalpha << (r1 <= r2) << '\n';
    else if (op == ">=")
     std::cout << std::boolalpha << (r1 >= r2) << '\n';
    else if (op == "+")
     std::cout << (r1 + r2) << '\n';
    else if (op == "-")
     std::cout << (r1 - r2) << '\n';
    else if (op == "*")
     std::cout << (r1 * r2) << '\n';
    else if (op == "/")
     std::cout << (r1 / r2) << '\n';
    else
     std::cerr << "invalid operator: " << op << '\n';

  }

  // If we got to the end of the file without fatal errors,
  // return success.
  if (std::cin.eof())
    return 0;

  // Otherwise, diagnose errors in input and exit with an error
  // code.
  if (std::cin.fail()) {
    std::cerr << "input error\n";
    return 1;
  }

  return 0;
}

Answer 1

#include s你的rational.hpp每個翻譯單元都將得到比較運算符函數的定義，這肯定會導致鏈接時的重復定義。

嘗試在他們面前貼上“內聯”關鍵字。

Answer 2

您在rational.hpp定義函數，這意味着每個翻譯單元都包含rational.hpp將包含定義，並導致重復的定義錯誤。

您應該將聲明和定義編入頭文件和實現文件中。 如，

rational.hpp：

bool operator==(Rational a, Rational b);
bool operator!=(Rational a, Rational b);
...

rational.cpp：

bool operator==(Rational a, Rational b){
        return (a.n == b.n && a.d == b.d);
}
bool operator!=(Rational a, Rational b){
        return (a.n != b.n && a.d != b.d);
}
...

BTW： operator!=的邏輯operator!=似乎是錯的，我想它可能是return (an != bn || ad != bd); 。 無論如何，正如@NickyC建議的那樣，最好將其作為return !(a == b);來實現return !(a == b); 避免重復。