Question

#include <iostream>
#include <cstring>
#include <fstream>
#include <cstdlib>

using namespace std;

class SurnameInfo
{
private:
    char *name;
    int counter;
    float pctrace[6];
public:
    char getname(){ return *name; };
    int getcounter(){ return counter; };
    float getpctrace(int i){ return pctrace[i]; };
    void setname(char*, int);
    void setcounter(int);
    void setpctrace(float, int);
    void printname() {cout << name; };
};
void SurnameInfo::setname(char * nm, int len)
{
    name = new char[len + 1];
    name = nm;
}
void SurnameInfo::setcounter(int ct)
{
    counter = ct;
}
void SurnameInfo::setpctrace(float prace, int i)
{
    pctrace[i] = prace;
}

int numberOfNames = 0;
const int MAXARRAY = 151671;
SurnameInfo * surnames[MAXARRAY];
const int MAXLINE = MAXARRAY;
void processLine(char *, int);
SurnameInfo * binarySeach(SurnameInfo **, int, char *);
void mostPopular(int);
void searchName();

int main()
{
    ifstream inputfile;
    inputfile.open("names.csv");
    char line[MAXLINE];
    if (!inputfile) return 0;
    inputfile.getline(line, MAXLINE);
    inputfile.getline(line, MAXLINE);
    while (!inputfile.eof())
    {
        processLine(line, numberOfNames++);
        inputfile.getline(line, MAXLINE);
    }

    cout << "Here is a list of names most exclusive to each race: " << endl;
    cout << "Press enter to continue.";
    cin.clear(); cin.sync(); cin.get();
    system("CLS");
    cout << "Highest Percentage: \n\nWHITE: \n";
    mostPopular(0);
    cout << "\n\nBLACK:\n";
    mostPopular(1);
    cout << "\n\nASIAN AND PACIFIC ISLANDER: \n";
    mostPopular(2);
    cout << "\n\nAMERICAN INDIAN OR ALASKAN NATIVE: \n";
    mostPopular(3);
    cout << "\n\n2 OR MORE RACES: \n";
    mostPopular(4);
    cout << "\n\nHISPANIC: \n";
    mostPopular(5);
    inputfile.close();
    cin.clear(); cin.sync(); cin.get();
    return 0;
}

void processLine(char *line, int n)
{
    surnames[n] = new SurnameInfo;
    char * pch = strtok(line, ",");
    int len = strlen(pch);
    surnames[n]->setname(pch,len);
    surnames[n]->setcounter(atoi(strtok(NULL, ",")));
    for (int i = 0; i < 6; i++)
    {
        pch = strtok(NULL, ",");
        surnames[n]->setpctrace(pch[0] == '(' ? -1 : atof(pch), i);
    }
}

void mostPopular(int race)
{
    const int TOPS = 20;
    int tops[TOPS + 1];
    int kept = 0;
    for (int i = 0; i < numberOfNames; i++)
    {
        if (surnames[i]->getcounter() < 10000) continue;
        int j = kept - 1;
        for (; j >= 0; j--)
        {
            if (surnames[i]->getpctrace(race) > surnames[tops[j]]->getpctrace(race))
                tops[j + 1] = tops[j];
            else break;
        }
        if (j + 1 < TOPS) tops[j + 1] = i;
        if (kept < TOPS) kept++;
    }
    for (int i = 0; i < TOPS; i++)
    {
        surnames[tops[i]]->printname(); 
        cout << " " << surnames[tops[i]]->getpctrace(race) << endl;
    }
}

在上面的行surnames[tops[i]]->printname();中，printname函数实际上并不打印名称，即使该函数放在程序的其他位置也能正常工作。我不能为我的生活找出原因。我知道我可能会有一些函数，而且程序顶部不会被调用。我还没有完成，但我需要弄清楚这里发生了什么。

Answer 1

我认为问题是：

在使用int tops[TOPS + 1];之前，您尚未初始化此阵列。如果数据不够，则无法通过for函数初始化数组。例如如果surnames[i]->getcounter() < 10000都为真，则tops数组将不会出现数据。然后你使用surnames[tops[i]]，可能会收到错误。
```
int tops[TOPS + 1] = {0}; // you may need to consider this problem.
```
在void SurnameInfo::setname(char * nm, int len)中，您将指针复制为nm，但指针nm指向您getline数据。在下一个getline之后，您name将指向下一行，因此您什么也得不到，因为它指向文件结束。
```
void SurnameInfo::setname(char * nm, int len)
{
    name = new char[len + 1];
    memset(name, len+1, 0);
    memcpy(name, nm, len);
}
SurnameInfo::~SurnameInfo()
{
     delete [] name;
}
```

类中的C ++打印功能不起作用

1 个答案: