c++ - 重新分配变量 C++

Question

我正在尝试将公共(public)变量 overallRating 重新分配给值 7。它在构造函数中最初设置为 0。我的代码可以编译，但是当我尝试访问另一个文件中的 schoolName.overallRating 时，它说 overallRating = 0 而不是 7。我的赋值语句有问题吗？ GradSchool 类仅包含学校列表。

学校.cc

#include "school.h"

School::School()
 {
   women = 0;
   rateAI = 0;
   rateSys = 0;
   rateTheory = 0;
   effectiveness = 0;
   ratePubs = 0;
   overallRating = 0;
 }

School::School (string myName, string myState, int theWomen, int myRateAI, int myRateSys,int myRateTheory, int myEffectiveness, int myRatePubs)
 {
   name = myName;
   state = myState;
   women = theWomen;
   rateAI = myRateAI;
   rateSys = myRateSys;
   rateTheory = myRateTheory;
   effectiveness = myEffectiveness;
   ratePubs = myRatePubs;
   overallRating = 0;
 }

void School::computeRating (int weightWomen, int weightAI, int weightSys, int weightTheory, int weightEffect, int weightPubs)
{
  overallRating = 7;
}

void School::printSchoolInfo ()
{
  cout<<"Name: "<<name<<endl;
  cout<<"State: "<<state<<endl;
  cout<<"Rating of number of women PhD's: "<<women<<endl; 
  cout<<"Rating of AI program: "<<rateAI<<endl;
  cout<<"Rating of Systems program: "<<rateSys<<endl;
  cout<<"Rating of Theory program: "<<rateTheory<<endl;
  cout<<"Effctiveness rating: "<<effectiveness<<endl;
  cout<<"Rating of faculty publications: "<<ratePubs<<endl;
  cout<<"Overall rating: "<<overallRating<<endl;
}

学校.h

#include <string>
#include <iostream>
using namespace std;

#ifndef SCHOOL_H
#define SCHOOL_H
class School {
  public:
    string name;      // name of the school
    string state;     // state in which school is located
    int women;      // rating of percentage of women PhD's (1 to 10)
    int rateAI;     // rating of AI program (1 to 10)
    int rateSys;      // rating of Computer Systems program (1 to 10)
    int rateTheory;   // rating of Theory program (1 to 10)
    int effectiveness;  // rating of effectiveness in educating research scholars 
    int ratePubs;     // rating of impact of publications per faculty member 
    int overallRating;  // overall rating that considers all of the above factors 

    School ();
    School (string myName, string myState, int theWomen, int myRateAI, int myRateSys,
        int myRateTheory, int myEffectiveness, int myRatePubs);
    void printSchoolInfo ();
    void computeRating (int weightWomen, int weightAI, int weightSys, 
                int weightTheory, int weightEffect, int weightPubs);
};    
#endif

主要

 //
// gradSchoolTest.cc
//
// code to test the creation of a GradSchools object that stores and sorts
// multiple instances of a School
#include <iostream>
#include "gradSchools.h"
#include "gradSchools.cc"
#include "school.h"
#include "school.cc"
#include "sortable_list.h"
#include "sortable_list.cc"
#include "list.h"
#include "list.cc"
using namespace std;

GradSchools makeGradSchools () {
    // Note that the ratings here are somewhat arbitrary
    GradSchools newSchools;
    newSchools.addSchool("MIT", "Massachusetts", 5, 10, 9, 10, 10, 7);
    newSchools.addSchool("Stanford", "California", 9, 8, 5, 8, 10, 9);
    newSchools.addSchool("CMU", "Pennsylvania", 6, 9, 9, 7, 8, 6);
    newSchools.addSchool("UC Berkeley", "California", 4, 6, 8, 9, 9, 9);
    newSchools.addSchool("Cornell", "New York", 9, 5, 8, 9, 9, 8);
    newSchools.addSchool("Univ. of Illinois", "Illinois", 4, 7, 7, 7, 7, 7);
    newSchools.addSchool("Univ. of Washington", "Washington", 7, 5, 7, 8, 8, 8);
    newSchools.addSchool("Princeton", "New Jersey", 8, 4, 5, 8, 7, 10);
    return newSchools;
} //makeGradSchools

int main (void) {
    GradSchools myGradSchools = makeGradSchools();
    int weightWomen = 5;
    int weightAI = 5; 
    int weightSys = 2;
    int weightTheory = 0;
    int weightEffectiveness = 5;
    int weightPubs = 4;
    myGradSchools.rankSchools(weightWomen, weightAI, weightSys, weightTheory, weightEffectiveness, weightPubs);
    cout << endl;
    myGradSchools.rankSchoolsFactor("AI");
    myGradSchools.rankSchoolsFactor("women");
    myGradSchools.printGradSchools();

    return 0;
} //end main

研究生院

#include "gradSchools.h"

/*Implement functions from gradSchools.h file here */
GradSchools::GradSchools()
 {
   schools.clear();
 }
void GradSchools::addSchool (string name, string state, int women, int rateAI, int rateSys,int rateTheory, int effect, int ratePubs)
 {   
schools.insert(schools.size(), (School(name, state, women, rateAI, rateSys, rateTheory, effect, ratePubs)));
 }

void GradSchools::computeRatings (int weightWomen, int weightAI, int weightSys, int weightTheory, int weightEffect, int weightPubs)
 {
 for (int i = 0; i < schools.size()-1; i++)
     {
       School entry;
       schools.retrieve(i, entry);
       entry.computeRating(weightWomen, weightAI, weightSys, weightTheory, weightEffect, weightPubs);
     }
 }
void GradSchools::rankSchools (int weightWomen, int weightAI, int weightSys, int weightTheory, int weightEffect, int weightPubs)
 {
   computeRatings(weightWomen, weightAI, weightSys, weightTheory, weightEffect, weightPubs);
   schools.selection_sort();
   for (int i = schools.size()-1; i>= 0; i--)
     {
       School x;
       schools.retrieve(i, x);
       cout<<x.name<<endl;
     }

 }
void GradSchools::rankSchoolsFactor (string factor)
 {

 } 

void GradSchools::printGradSchools()
 {
   for (int i = 0; i < schools.size()-1; i++)
     {
       School entry;
       schools.retrieve(i, entry);
       entry.printSchoolInfo();
       cout<<endl;
     }
 }

检索

template<class List_entry>
Error_code List<List_entry> :: retrieve(int position, List_entry &x ) const
  /*Post: If 0¾ position < n, where n is the number of entries in the List,
  the function succeeds: The entry at position is copied to x; all
  List entries remain unchanged.
  Else: The function fails with a diagnostic error code.*/
{
  if (position < 0 || position >= count) {
    return range_error;
  }
  x = entry[position];
  return success;
} //retrieve

Answer 1

   School entry;
   schools.retrieve(i, entry);
   entry.computeRating(weightWomen, weightAI, weightSys, weightTheory, weightEffect, weightPubs);

虽然在您的代码中不可见，但我想 schools 是一些集合，函数 retrieve 检索数组中的一些元素。

问题是您上面的代码适用于条目的拷贝，而不是条目本身。因此，schools 集合中的元素未被修改，因为 computeRating 是在 copied entry 变量上调用的，不是元素本身。

要完全修复您的代码，我们需要查看retrieve 的工作原理，并以某种方式修改它，以便我们可以获得对元素的引用，而不是复制。

建议:修改您的retrieve 函数，以便它返回对元素的引用。换句话说，让它具有以下签名:

School& retrieve(int i);

之后，以这种方式修改引用的代码:

    School& entry = schools.retrieve(i);
    entry.computeRating(weightWomen, weightAI, weightSys, weightTheory, weightEffect, weightPubs);

编辑 看到你的检索函数后，如果它真的需要结果作为一个输出参数，你仍然可以

Error_code List<List_entry> :: retrieve(int position, List_entry*& x ) const // set the output param as a pointer
{
  if (position < 0 || position >= count) {
    return range_error;
  }
  x = &entry[position]; // return a pointer
  return success;
} 

之后，引用的代码变为:

    School* entry;
    schools.retrieve(i, entry);
    entry->computeRating(weightWomen, weightAI, weightSys, weightTheory, weightEffect, weightPubs);