在我的代码中被零除

Question

这是我的代码，我不知道我在哪里得到零除问题。

mreviewApp.cpp

const int SIZE = 80;
const char DELIMIT = '|';

void parseLine(const char line[], string& title, int& rating);
void stringTrim(char st[]);
void printMrList(std::vector <Mreview> mrList);
Mreview searchTitle(std::vector <Mreview> &mrList, string title);


int main()
 {
  ifstream fin;

  fin.open("rating_list.txt");
  if (fin.fail()) {
    cerr << "Input file opening error.\n";
    exit(1);
  }

  char line[SIZE];
  string title;
  int rating;
  int lineCount = 0;

  std::vector <Mreview> mrList;

  /* Process one line at a time */
  // Read the first line
  fin.getline(line, SIZE);
  stringTrim(line);

  // Process loop
  while (strlen(line) != 0) { 
    parseLine(line, title, rating);
    lineCount++;

    Mreview review = searchTitle(mrList, title);
    review.addScore(rating);

    // Read the next line
    fin.getline(line, SIZE);
    stringTrim(line);
  }

  cout << "** PROCESS DONE. There were " << mrList.size() << " movie titles. **\n\n";

  printMrList(mrList);
  // Close the input file before exit.
  fin.close();

  system("Pause");
  return 0;
}

void parseLine(const char line[], string& title, int& rating)
{
  char s[SIZE], r[SIZE];
  const char *ptr, *temp1;
  char *temp2;

  ptr = strchr(line, DELIMIT);

  if (ptr != NULL) {
    // First grab the title string (until '|').
    temp1 = line;
    temp2 = s;
    while (temp1 != ptr)
      *temp2++ = *temp1++;

    *temp2 = '\0';

    stringTrim(s);
    title = s;

    // Second grab the rating number
    temp1 = ptr+1;
    temp2 = r;
    while (*temp1 != '\0')
      *temp2++ = *temp1++;

    *temp2 = '\0';

    stringTrim(r);
    rating = atoi(r);
  }
  else {
    title = "";
    rating = 0;
  }
}

void stringTrim(char st[])
{
  char* ptr;

  for (ptr = st; *ptr; ptr++) ;
  for (ptr--; *ptr == ' ' && ptr >= st; ptr--) ;
  ptr++;
  *ptr = '\0';

  for (ptr = st; *ptr && *ptr == ' '; ptr++) ;

  if (*ptr && ptr != st) {
    char* ptr2;
    for (ptr2 = st; *ptr; *ptr2++ = *ptr++) ;
    *ptr2 = '\0';
  }
}

void printMrList(std::vector <Mreview> mrList)
{
    std::vector<Mreview>::iterator itr;
    for(itr = mrList.begin(); itr != mrList.end(); itr++) {
        Mreview review = *(itr);
        cout << review.getTitle() << "\t\t" << review.getTotalScore() << "\t\t" << review.aveRating() << endl;
    }
}

Mreview searchTitle(std::vector <Mreview> &mrList, string title)
{
    Mreview review (title); 
    std::vector<Mreview>::iterator itr;
    for(itr = mrList.begin(); itr != mrList.end(); itr++) {
        Mreview r2d2 = *(itr);
        if(review.getTitle() == r2d2.getTitle())
            return r2d2;
    }
    mrList.push_back(review);
    return review;
}

mreview.cpp

Mreview::Mreview(string ttl)
  : title(ttl), totalScore(0), numRatings(0) {}

Mreview::Mreview(string ttl, int score)
  : title(ttl), totalScore(score), numRatings(1) {}
void Mreview::addScore(int score)
{
    this->totalScore += score;
    this->numRatings += 1;
}

double Mreview::aveRating() const
{
    double rating = totalScore/numRatings;
    return rating;
}

mreview.h

#ifndef MREVIEW_H
#define MREVIEW_H

#include <string>
using namespace std;

class Mreview
{
public:
  Mreview(string ttl = "N/A");
  Mreview(string ttl, int firstScore);

  string getTitle() const { return title; }
  int getTotalScore() const { return totalScore; }
  int getNumRatings() const { return numRatings; }

  void addScore(int score);
  double aveRating() const;

private:
  string title;
  int totalScore;
  int numRatings;
};

#endif

我的问题是我无法弄清楚要解决的问题。 我已经阅读了评论，但仍然感到困惑。

Answer 1

您正在分配（并复制！） Mreview对象的向量， 所有这些对象都使用默认的ctor构造 ，因此numRatings默认为0，并且您没有做任何事情来确保从未在未修改的对象上调用aveRating()或至少保护自己不受numRatings为0的影响。

编辑：最简单的解决方法：

double Mreview::aveRating() const { 
    if (numRatings == 0)
        return 0.;
    else 
        return static_cast<double>(totalScore)/numRatings;
}

进一步的修正，IMO，将存储Mreview 指针 （理想的shared_ptr）在矢量和new荷兰国际集团它们当第一得分要而非前面添加 。

Answer 2

我只看到一个实际的除法运算...

double Mreview::aveRating() const { 
   double rating = totalScore/numRatings; 
   return rating; 
}

...在那里吗？

Answer 3

寻找除零问题时，请寻找/和％运算符。 我在您的代码中只看到一个/。

Answer 4

不是除以零的错误，而是...

double Mreview::aveRating() const
{
    double rating = totalScore/numRatings;
    return rating;
}

您要获取两个整数值并将其存储在double中，而无需进行类型转换...您必须将totalScore或numRatings强制转换为double，如：

double Mreview::aveRating() const
{
    double rating = (double)totalScore/numRatings;
    return rating;
}

Answer 5

您可以在调试器中运行它，然后告诉陷阱发生的位置吗？

Answer 6

它看起来像如果线的长度修整后为0，然后printMrList()可以在不称为review.addScore()第一被调用。 在这种情况下， printMrList()调用review.aveRating() ，尝试将totalScore除以numRatings 。 这两个值均为0，因此会出现被零除的错误。