Why can't I insert values in an array of objects of a structure?

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I have this block of code, -collection- is my fstream object and -students- is a structure I made. I made -file[ctr]- which is an array of objects of students, when I build and run it, the IDE I use which is Code::Blocks don't give me errors. The error message [fileprocessing.exe has stopped working. A problem caused the program to stop working correctly...etc.] appears after I fill up firstname. Any idea to what may be wrong with my code?

C++

if(choice2=='A'||choice2=='a'){
    students file[ctr];
    cout<<"Student ID: ";
    cin>>file[ctr].studentID;
    cout<<"Surname: ";
    cin>>file[ctr].surname;
    cout<<"Firstname: ";
    cin>>file[ctr].firstname;
    cout<<"Birthdate: ";
    cin>>file[ctr].birthdate;
    cout<<"Sex: ";
    cin>>file[ctr].sex;
    fstream collection(filename, std::fstream::in | std::fstream::out | std::fstream::app);
    collection<<ctr
    <<"\t"<<file[ctr].studentID
    <<"\t"<<file[ctr].surname
    <<"\t"<<file[ctr].firstname
    <<"\t"<<file[ctr].birthdate
    <<"\t"<<file[ctr].sex
    <<endl;
    collection.close();
    ctr++;
    system("cls");
}

What I have tried:

C++

int ctr=1;
if(choice2=='A'||choice2=='a'){
    students file;
    cout<<"Student ID: ";
    cin>>file.studentID;
    cout<<"Surname: ";
    cin>>file.surname;
    cout<<"Firstname: ";
    cin>>file.firstname;
    cout<<"Birthdate: ";
    cin>>file.birthdate;
    cout<<"Sex: ";
    cin>>file.sex;
    fstream collection(filename, std::fstream::in | std::fstream::out | std::fstream::app);
    collection<<ctr<<"\t"<<file.studentID
                        <<"\t"<<file.surname
                        <<"\t"<<file.firstname
                        <<"\t"<<file.birthdate
                        <<"\t"<<file.sex
                        <<endl;
    collection.close();
    ctr++;
    system("cls");
}

Simple, I just removed the [ctr]s and it works well, but I know it's going to cause me problems when I work on the other parts of my system. I have to make an array of objects because I have a collection of student data in a collection of text files and they shouldn't be of a students object... Please help!

Posted 20-Aug-16 0:21am

mariaclara

Updated 20-Aug-16 1:27am

Richard MacCutchan

v2

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Richard MacCutchan · Accepted Answer · 2016-08-20T01:27:00

C++

students file[ctr];
cout<<"Student ID: ";
cin>>file[ctr].studentID;

That is wrong; you are declaring an array of students objects, and immediately using the count as an index into the array (valid array indices go from 0 to count - 1). So in this case it means that the structure you create will be overwriting your memory and ultimately cause some random event, such as an application crash. You should do it like:

C++

int count; // the number of elements in the array
// initialise count somehow

// declare the array of 'count' elements
students file[count];

// now use a loop to fill the array
int ctr;
for (ctr = 0; ctr < count; ++ctr)
{
    cout<<"Student ID: ";
    cin>>file[ctr].studentID;
// ... etc
} // end of for loop