c++ - 当其标识符已经是结构的成员时如何使用枚举器列表项？

Question

我的程序没有响应。当我运行该程序时，它停留在空白屏幕上，没有错误也没有输出。

我不知道是什么错误。如何从结构内部读取枚举器。以下是错误的。请帮忙。

infile >> gRecs[i].Subjects[j].Status;

Error:

C:\Users\PC\Desktop\a1\ass1.cpp [Error] no match for 'operator>>' 
(operand types are 'std::ifstream {aka std::basic_ifstream<char>}' and 
'StatusType')

这是“.txt”文件。

7453842   
Gregory  Harrison   
4   
CSCI104 0 56  
IACT111 0 44  
INFO112 0 75  
CSCI321 0 89

输出必须是这样的:

13 records read
Commands Available:
d - Display Record
u - Update Record
q - Quit the program
Command: d
Enter student number: 4734455
Student No. 4734455
First Name Kieren
Last Name Legrande
Subjects:
CSCI104 Provisional 65
IACT123 Enrolled 67
CSCI121 Enrolled 98

我想读取此数据并保存并更新记录。但是，该程序不会运行或停留在空白屏幕上，同时没有显示任何错误。它运行但不输出任何内容。

.h 和 main.cpp 都很好。 但我对这个编码文件有疑问。 这是我的编码:

#include <iostream>
#include <fstream>
using namespace std;
// ============== Constants ==========================================

const char cTextFileName[]   = "ass1.txt";
const char cBinaryFileName[] = "ass1.dat";
const int cMaxRecs = 100;
const int cMaxChars = 30;
const int cMaxSubjects = 8;

// ============= User Defined types ==================================

enum StatusType{eEnrolled,eProvisional,eWithdrawn};
struct SubjectType{ char Code[8]; StatusType Status; int Mark;};

struct StudentRecord{
    long StudentNo;
    char FirstName[cMaxChars];
    char LastName[cMaxChars];
    int NumSubjects;
    SubjectType Subjects[cMaxSubjects];
};


// ============= Global Data =========================================

StudentRecord gRecs[cMaxRecs];
int gNumRecs=0;


// ============= Private Function Prototypes =========================

void PrintRecord(int i);
int FindRecord(long StudentNum);

// ============= Public Function Definitions =========================


void ReadFile()
{ // Reads data file into array

int i =0;
StatusType items;

ifstream infile;
infile.open("ass1.txt");
if (!infile.good())
{
    cerr << "There is an error opening a file.";
    exit(1);
}
infile >> gRecs[i].StudentNo;
while(!infile.eof())
{
    infile >> gRecs[ i].FirstName;
    infile >> gRecs[i].LastName;
    infile >> gRecs[i].NumSubjects;
    for(int j=0; j<=gRecs[i].NumSubjects;)
    {
    infile >> gRecs[i].Subjects[j].Code;

    infile >> gRecs[i].Subjects[j].Status;


    infile >> gRecs[i].Subjects[j].Mark;
    }
    i++;
    infile >> gRecs[i].StudentNo;  

    gNumRecs = i;
    infile.close();
    cout << gNumRecs << "read records " << gNumRecs;

}

}

void DisplayRecord()
{    // Displays specified record on screen

//  int stuNo;
    int i = 0;
//  int StudentNo;

//  cout << PrintRecord(i);
    cout << "Enter Student Number :";
    cin >> gRecs[i].StudentNo;

    i=FindRecord(gRecs[i].StudentNo);
    if(!FindRecord(gRecs[i].StudentNo));
    {
     cout << "Sorry, Record not found .";
}
PrintRecord(i);    

//  cout << PrintRecord(i);


}

void SaveFile()
{// Writes array to text data file

StatusType Status;
fstream myfile;
myfile.open("ass1.txt");
if (!myfile.good())
{
    cerr << " Problem opening the data file.";
    exit(1);
}

for(int i=0; i<gNumRecs;)
{
    cout << "Student No :"   << gRecs[i].StudentNo;
    cout << "First Name :"   << gRecs[i].FirstName;
    cout << "Last Name  :"   << gRecs[i].LastName;
    cout << "Subjects   :"   << gRecs[i].NumSubjects;

    for(int j=0; j<=gRecs[i].NumSubjects;)
    {
    cout << gRecs[i].Subjects[j].Code << "  ";

    switch(Status)
    {
        case eEnrolled    : cout << "Enrolled"    << "  " << endl; break;
        case eProvisional : cout << "Provisional" << "  " << endl; break;
        case eWithdrawn   : cout << "Withdrawn"   << "  " << endl; break;
    }   
    cout << gRecs[i].Subjects[j].Mark;
    }
}
myfile.close();

cout << "Records have been saved.";

}

void UpdateRecord()
{// updates status or mark of specified subject of specified student number

int i=0;
int j=0;
//  int sub_cod;
int studentNo;
//  int stuNo;
char optn;
char s;
int m;

fstream infile;
infile.open("ass1.txt");
cout << "Enter Student Number :";
cin >> gRecs[i].StudentNo;
infile >> gRecs[i].StudentNo;

i=FindRecord(gRecs[i].StudentNo);
if(!FindRecord(gRecs[i].StudentNo))
{
    cout << "Sorry, Record not found .";
}

PrintRecord(i);
cout << "Please Enter the subject code you want to update :";
cin  >> gRecs[i].Subjects[j].Code;
if(!gRecs[i].Subjects[j].Code)
{
    cout << "Subject code not found!";
}
cout << "Select status or mark (s/m) :";
cin  >> optn;

switch(optn)
{

case 's':
    cout << "Select new status :" ;
    cout << "    "  << "e: Enrolled";
    cout << "    "  << "p: Provisional ";
    cout << "    "  << "w: Withdrawn ";
    cin  >> s;
    // need to be entered
    cout << "Status :" << s << endl;
    cout << "Record "  << i << "updated ." << endl;
    break;

case 'm':
    cout << "Enter the marks";
    cin  >> m;

    for(int j=0; j<=gRecs[i].NumSubjects;)
    {

    infile >> gRecs[i].Subjects[j].Mark;
    }
    break;

}


}


// ============= Private Function Definitions =========================

void PrintRecord(int i)
{ // Prints record i on screen

StatusType emembers;
cout << gRecs[i].StudentNo;
cout << gRecs[i].FirstName;
cout << gRecs[i].LastName;
cout << gRecs[i].NumSubjects;
for(int j=0; j<=gRecs[i].NumSubjects;)
    {
    cout << gRecs[i].Subjects[j].Code;

/*      switch(emembers)
    {
        case '0'   : cout << "Enrolled"    ; break;
        case '1'   : cout << "Provisional" << endl; break;
        case '2'   : cout << "Withdrawn"   << endl; break;
    }
*/
    cout << gRecs[i].Subjects[j].Mark;
    }

}

int FindRecord(long StudentNo)
{// returns index of matching record or -1 if not found
int i=0;
for(int i=0; i<13;)

{
    if (!gRecs[i].StudentNo && StudentNo == StudentNo)
    {
        return i;
    }

}

return -1;

}

另外，我对 UpdateRecord() 和 FindRecord() 有疑问。如果我犯了任何错误，请检查错误。请大伙帮忙。谢谢

Answer 1

您应该为您的自定义类型覆盖 operator >>。

template<class _CharT,class _Traits>
std::basic_istream<_CharT,_Traits>&
 operator >>(std::basic_istream<_CharT, _Traits>& _is, StatusType& _my_enum)
{
    int _temp;
    _is >> _temp;
    _my_enum = static_cast<StatusType>(_temp);
    return _is;
}