I am trying to write a program that reads information from a text file and copies it into an array using structs and unions and cstrings. My textfile looks something like this.
F South Korea
Male Psy Park Jae Sang
31 - 12 - 1977
3 CSCI114 55 CSCI103 44 GangNam 100
S Female Super Junior
5 - 8 - 1978
2 CSCI114 60 CSCI103 80
F People Republic Of China
Unknown James Bond
11 - 12 - 1976
4 CSCI114 54 CSCI124 66 CSCI007 99 CSCI123 28
My query is, I’ve written a simple switch case with a for loop that reads in the information based on its criteria. For instance, the first letter before each paragraph denotes whether the student is a Foreigner, F, or Singaporean, S. Based to their nationality, I’m choosing which struct/union to copy their information into. To give you a better idea, this is what my final text output file will look like after I take in the information from the original text file and process it.
https://i.stack.imgur.com/Bv2YS.jpg
Below is my section of code I am having trouble with. It seems whether or not the char variable reads “S” or “F”, my switch statement is only reading it in as “F”.
//file to array.
char dateJunk;
int numOfCourses;
int k = 0;
while (!afile.eof())
{
for (int k = 0; k < 3; k++)
{
afile >> locale;
switch (locale)
{
case 'F':
afile.getline(x[k].st.foreignStudent.nationality, MAX);
afile >> x[k].st.foreignStudent.gender;
afile.getline(x[k].st.foreignStudent.name, MAX);
afile >> x[k].st.foreignStudent.bd.day;
afile >> dateJunk;
afile >> x[k].st.foreignStudent.bd.month;
afile >> dateJunk;
afile >> x[k].st.foreignStudent.bd.year;
afile >> x[k].st.foreignStudent.numOfCourses;
for (int i = 0; i < x[k].st.foreignStudent.numOfCourses; i++)
{
afile >> x[i].st.foreignStudent.subjects[k];
afile >> x[i].st.foreignStudent.grades[k];
}
break;
case 'S':
afile >> x[k].st.localStudent.gender;
afile.getline(x[k].st.localStudent.name, MAX);
afile >> x[k].st.localStudent.bd.day;
afile >> dateJunk;
afile >> x[k].st.localStudent.bd.month;
afile >> dateJunk;
afile >> x[k].st.localStudent.bd.year;
afile >> x[k].st.localStudent.numOfCourses;;
for (int i = 0; i < x[k].st.localStudent.numOfCourses; i++)
{
afile >> x[i].st.localStudent.subjects[k];
afile >> x[i].st.localStudent.grades[k];
}
}
}
}
//Tests my cstring arrays to see everything is copied in correctly.
for (int k = 0; k < 3; k++)
{
cout << locale << " " << x[k].st.foreignStudent.nationality;
cout << endl;
cout << x[k].st.foreignStudent.gender;
cout << x[k].st.foreignStudent.name;
cout << endl;
cout << x[k].st.foreignStudent.bd.day << " - ";
cout << x[k].st.foreignStudent.bd.month << " - ";
cout << x[k].st.foreignStudent.bd.year;
cout << endl;
cout << x[k].st.foreignStudent.numOfCourses;
cout << endl;
for(int i = 0; i < x[k].st.foreignStudent.numOfCourses; i++)
{
cout << x[i].st.foreignStudent.subjects[k] << " ";
cout << x[i].st.foreignStudent.grades[k] << " ";
}
cout << endl;
}
return 0;
}
Below is the code in its entirety.
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
using namespace std;
const int MAX = 80;
struct Birthday
{
char day[MAX];
char month[MAX];
char year[MAX];
};
struct Local
{
char name[MAX];
char nationality[MAX];
char gender[MAX];
Birthday bd;
char subjects [MAX][MAX];
char grades [MAX][MAX];
int numOfCourses;
};
struct Foreigner
{
char name[MAX];
char nationality[MAX];
char gender[MAX];
Birthday bd;
char subjects [MAX][MAX];
char grades [MAX][MAX];
int numOfCourses;
};
union Student
{
Local localStudent;
Foreigner foreignStudent;
};
enum CountryType {S, F};
struct UowStudents
{
CountryType ct;
Student st;
};
int fileToArray (fstream& afile, char fileName [], UowStudents* x, char& locale);
int main ()
{
srand(time_t(NULL));
fstream afile;
UowStudents x [MAX];
char fileName[MAX];
char locale;
cout << "Enter filename: ";
cin >> fileName;
int size = fileToArray (afile, fileName, x, locale);
}
int fileToArray (fstream& afile, char fileName [], UowStudents* x, char& locale)
{
afile.open(fileName, ios::in);
if (!afile)
{
cout << fileName << "could not be opened for read" << endl;
exit (-1);
}
//file to array.
char dateJunk;
int numOfCourses;
int k = 0;
while (!afile.eof())
{
for (int k = 0; k < 3; k++)
{
afile >> locale;
switch (locale)
{
case 'F':
afile.getline(x[k].st.foreignStudent.nationality, MAX);
afile >> x[k].st.foreignStudent.gender;
afile.getline(x[k].st.foreignStudent.name, MAX);
afile >> x[k].st.foreignStudent.bd.day;
afile >> dateJunk;
afile >> x[k].st.foreignStudent.bd.month;
afile >> dateJunk;
afile >> x[k].st.foreignStudent.bd.year;
afile >> x[k].st.foreignStudent.numOfCourses;
for (int i = 0; i < x[k].st.foreignStudent.numOfCourses; i++)
{
afile >> x[i].st.foreignStudent.subjects[k];
afile >> x[i].st.foreignStudent.grades[k];
}
break;
case 'S':
afile >> x[k].st.localStudent.gender;
afile.getline(x[k].st.localStudent.name, MAX);
afile >> x[k].st.localStudent.bd.day;
afile >> dateJunk;
afile >> x[k].st.localStudent.bd.month;
afile >> dateJunk;
afile >> x[k].st.localStudent.bd.year;
afile >> x[k].st.localStudent.numOfCourses;;
for (int i = 0; i < x[k].st.localStudent.numOfCourses; i++)
{
afile >> x[i].st.localStudent.subjects[k];
afile >> x[i].st.localStudent.grades[k];
}
}
}
}
//Tests my cstring arrays to see everything is copied in correctly.
//The print for foreign student cstrings also has information for the
//one Singaporean student "S" in the middle. Singaporean must go into
//the local cstrings.
for (int k = 0; k < 3; k++)
{
cout << locale << " " << x[k].st.foreignStudent.nationality;
cout << endl;
cout << x[k].st.foreignStudent.gender;
cout << x[k].st.foreignStudent.name;
cout << endl;
cout << x[k].st.foreignStudent.bd.day << " - ";
cout << x[k].st.foreignStudent.bd.month << " - ";
cout << x[k].st.foreignStudent.bd.year;
cout << endl;
cout << x[k].st.foreignStudent.numOfCourses;
cout << endl;
for(int i = 0; i < x[k].st.foreignStudent.numOfCourses; i++)
{
cout << x[i].st.foreignStudent.subjects[k] << " ";
cout << x[i].st.foreignStudent.grades[k] << " ";
}
cout << endl;
}
//as you can see, everything gets copied into localStudent struct as well.
for (int k = 0; k < 3; k++)
{
cout << x[k].st.localStudent.gender;
cout << x[k].st.localStudent.name;
cout << endl;
cout << x[k].st.localStudent.bd.day << " - ";
cout << x[k].st.localStudent.bd.month << " - ";
cout << x[k].st.localStudent.bd.year;
cout << endl;
cout << x[k].st.localStudent.numOfCourses;
cout << endl;
for(int i = 0; i < x[k].st.localStudent.numOfCourses; i++)
{
cout << x[i].st.localStudent.subjects[k] << " ";
cout << x[i].st.localStudent.grades[k] << " ";
}
cout << endl;
}
return 0;
}
You are seeing the effects of using a
unionin C++.The main characteristic of a union that all members share the same block of memory. And because your member structures
LocalandForeignerhave exactly the same layout, you can use either to print the contents of the union.If you change one of the structures (for example, remove
nationalityfromLocal), you will see that some of the printouts get garbled (notably, those entries where you print a foreign student as a local one of vice versa). This is because the memory block used for the students get interpreted differently for local and foreign students.Note: Technically, this results in undefined behaviour, but in this case the results are unlikely to be catastrophic. Officially, you can only read the same member of a union that you last wrote to, or (if the members are structures) the initial members of a structure that are the same as in the structure last written to the union.