i am having difficulty understanding how to pass a file into a function.
i have a file with 20 names and 20 test scores that needs to be read by a function. the function will then assign the names and scores to a structure called student.
my question is how would i write a function call with the appropriate parameters. ? to make my function read the data in the file. thanks.
CODE
// ask user for student file
cout << "Enter the name of the file for the student data to be read for input" << endl;
cout << " (Note: The file and path cannot contain spaces)" << endl;
cout << endl;
cin >> inFileName;
inFile.open(inFileName);
cout << endl;
// FUNCTION CALL how do i set this up properly?
ReadStudentData(inFile, student, numStudents );
void ReadStudentData(ifstream& infile, StudentType student[], int& numStudents)
{
int index = 0;
string lastName, firstName;
int testScore;
while ((index < numStudents) &&
(infile >> lastName >> firstName >> testScore))
{
if (testScore >= 0 && testScore <= 100)
{
student[index].studentName = lastName + ", " + firstName;
student[index].testScore = testScore;
index++;
}
}
numStudents = index;
}
The way you pass an ifstream into the function is perfectly fine.
I suspect that the problem lies in the way you are managing your array of StudentType and its size (numStudents). I would recommend changing your code to use an std::vector instead of a raw array. In general, you should always prefer vectors over arrays unless you have a really good reason to use an array.
vectors can grow to accommodate more data and keep track of their size, so you don't have to.
Also, it's a good idea for functions to return objects rather than modify objects passed through the parameter list.
#include <vector>
using namespace std;
vector<StudentType> ReadStudentData(ifstream& infile) {
vector<StudentType> students;
string lastName, firstName;
int testScore;
while (infile >> lastName >> firstName >> testScore) {
if (testScore >= 0 && testScore <= 100) {
StudentType student;
student.studentName = lastName + ", " + firstName;
student.testScore = testScore;
students.push_back(student);
}
}
return students;
}
// call the function
vector<StudentType> students = ReadStudentData(infile);
// or if you have a C++11 compiler
auto students = ReadStudentData(infile);
// use students.size() to determine how many students were read
The reference to the file object seems to be fine, but the array of StudentType objects maybe wrong.
Try this:
void ReadStudentData(ifstream& infile,
std::vector<StudentType>& vecStudents,
int& numStudents)
Related
How can I ignore the first line of the text file and start at the second line when I called it in the code? I was wondering how. Also, how can I sort the file according to first name, last name and grade? I just have the first name sorted but not the last name and grade accordingly. If you have any idea, I hope you can share it with me. Thanks for the help! Here's my code:
#include <iostream>
#include <fstream>
using namespace std;
struct studentRecord{
string lastname;
string firstname;
string grade;
};
int main(){
ifstream ifs("student-file.txt");
string lastname, firstname, grade, key;
studentRecord records[20];
if(ifs.fail()) {
cout << "Error opening student records file" <<endl;
exit(1);
}
int i = 0;
while(! ifs.eof()){
ifs >> lastname >> firstname >> grade;
records[i].lastname = lastname;
records[i].firstname = firstname;
records[i].grade = grade;
i++;
}
for (int a = 1, b = 0; a < 20; a++) {
key = records[a].firstname ;
b = a-1;
while (b >= 0 && records[b].firstname > key) {
records[b+1].firstname = records[b].firstname;
b--;
}
records[b+1].firstname = key;
}
for (int k = 0; k < 20; k++) {
cout << "\n\t" << records[k].firstname << "\t"<< records[k].lastname << "\t" << records[k].grade;
}
}
When I saw this post it reminded me of a similar task completed at uni. I have rewritten your code to perform the same task but using classes instead of structs. I have also included a way to sort the vector by using the function here.
I have included the "ignore first line" method #Scheff's Cat mentioned.
Here it is:
#include <iostream>
#include <fstream>
#include <sstream>
#include <limits>
#include <string>
#include <vector>
using namespace std;
class studentrecord{
string firstname, lastname, grade;
public:
studentrecord(string firstname, string lastname, string grade){
this -> firstname = firstname;
this -> lastname = lastname;
this -> grade = grade;
}
friend ostream& operator<<(ostream& os, const studentrecord& studentrecord) {
os << "\n\t" << studentrecord.firstname << "\t" << studentrecord.lastname << "\t" << studentrecord.grade;
return os;
}
};
void displayRecords(vector <studentrecord*> records){
for(int i = 0; i < records.size(); i++){
cout << *records[i];
}
}
int main(){
//read in file
ifstream infile;
infile.open("student-file.txt");
infile.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
if (!infile.is_open()){
cout << "Error opening student records file" <<endl;
exit(1);
}
vector <studentrecord*> records;
string firstname, lastname, grade;
while (infile >> firstname >> lastname >> grade;) {
records.push_back(new studentrecord(firstname, lastname, grade));
}
displayRecords(records);
return 0;
}
To sort the vector so that it prints in order of either first name, last name or grade I used the following functions:
bool sortfirstname(studentrecord* A, studentrecord* B) {
return (A->getfirstname() < B->getfirstname());
}
bool sortlastname(studentrecord* A, studentrecord* B) {
return (A->getlastname() < B->getlastname());
}
bool sortgrade(studentrecord* A, studentrecord* B) {
return (A->getgrade() < B->getgrade());
}
sort(records.begin(), records.end(), (sortfirstname));
sort(records.begin(), records.end(), sortlastname);
sort(records.begin(), records.end(), sortgrade);
If you wanted to sort by first name you would call the sort(records.begin(), records.end(), (sortfirstname)); function and then the displayrecords() function.
The advantage of using classes stored in vectors is that you don't have to state the size of the vector containing the details about students since you can keep adding information to the end of the vector using the vector.push_back() function. It also makes sorting the data contained easier.
If anything isn't clear, let me know and I can give you a hand.
I made a topic a bit ago regarding structs. And I know that classes have the same concept as structs. How would I go about storing a string into the class?
This is the class
class studentType
{
public:
void setData(string, int);
string getName() const;
int getId() const;
private:
string name;
int sid;
};
void studentType::setData(string, int) {
name = ??;
sid = ??;
}
string studentType::getName() const {
return name;
}
int studentType::getId() const {
return sid;
}
The main consists of:
int main() {
studentType object, number;
cout << "enter name and code of item1: ";
cin >> object.setData() >> object.setData();
cout << "enter name and code for item2: ";
cin >> number.setData() >> number.setData();
system("pause");
return 0;
}
How would I fix the cin issue? I already have string defined in the header. And yes, I know using namespace std; isn't preferred but it's for simplicity
int id;
string name;
cout << "enter name and code of item1: ";
cin >> name >> id;
object.setData(name, id);
cout << "enter name and code for item2: ";
cin >> name >> id;
object.setData(name, id);
You should instead use a constructor for your class though:
class studentType {
public:
studentType(string name, int sid)
: name(name)
, sid(sid)
{ }
// ...
You can then initialize your objects with the correct name and ID:
cin >> name >> id;
studentType object(name, id);
But I suppose constructors will come up very soon in the tutorial or course you're currently doing.
cin >> object.setData() >> object.setData();
the >> operator doesn't call object.setData; it takes a reference and sets the reference contents to the extracted input. The expression object.setData() calls the function, which returns void. Of course, the >> operator cannot take a void argument. Also, there aren't enough arguments in the funcall because object.setData expects a string and an int.
You should do this:
std::string name;
int num;
cin >> name >> num;
object.setData(name, num);
Your setData function can be as such:
void studentType::setData(string name, int sid) {
this->name = name;
this->sid = sid;
}
And in your main():
First cin the values and then call the setData function, i.e.
int main(){
string name;
int code;
studentType object, number;
cout << "enter name and code of item1: ";
cin >> name >> code;
object = studentType();
object.setData(name, code);
// your remaining code
}
Just a note of caution:
If you use cin to get the name and code, the name can only be a single word. Say if you are writing a name of two words, the first word will be put in name and the second will be attempted to put in code.
In simpler terms, cin is space-delimited.
What you're looking for is std::getline(). I would use cin for getting your integers, but not for the strings. I would separate the user input like this. Like #Suhaib Ahmad said, cin is space-delimited. To get a string including spaces from stdin, use std::getline().
void studentType::setData(string n, int i) {
this->name = n;
this->sid = i;
}
-
int main(void) {
string n;
int i;
studentType object, number;
cout << "Enter name for item1: ";
getline(cin, n);
cout << "Enter code for item1: ";
cin >> i;
object = studentType(); // make sure you construct your studentType, I also recommend using a constructor function
object.setData(n, i);
cout << "Enter name for item2: ";
getline(cin, n);
cout << "Enter code for item2: ";
cin >> i;
number = studentType();
number.setData(n, i);
system("pause");
return 0;
}
The way you are using setData(), with no arguments given, as a place to store the cin input is incorrect. You would need to declare variables first, and then initialize your class with the variables.
I have a project in my C++ class - we're supposed to make a "simple student management system" comprised of a class for the student attribute variables, and a main function with a branch statement that lets the user input names and IDs for the students. I know that I need to use an array to make "slots" for the students, and that my branch statements need to let the user input values into those slots, but I'm not exactly sure how to do it. Here is the code that I have so far.
#include <string>
#include <iostream>
#include <utility>
using std::string;
using std::cin;
using std::cout;
using std::endl;
struct Student {
private:
int id;
string name;
int birthday;
public:
Student()
{
id = 0;
birthday = 0;
}
Student(int id, string name, int birthday)
{
//set your parameters to the class variables
this->id = id;
this->name = name;
this->birthday = birthday;
}
void setID(int id)
{
this->id = id;
}
int getID() {
return id;
}
void setName(string name)
{
this->name = name;
}
string getName()
{
return name;
}
void setBirthday(int birthday)
{
this->birthday = birthday;
}
int getBirthday()
{
return birthday;
}
void output() {
cout << id << name << birthday << endl;
}
};
int main() {
Student arr[50];
cout << "Student Management System" << endl;
cout << "Press 'a' to add a student" << endl;
char a = 1;
int y = 1;
while (a == 'a') {
switch (y)
{
cout << "Input Student ID:";
cin >> id;
}
}
}
What I'm focusing on most is the fourth line from the bottom. I was told that I need to use my setters, so I said that I want what my user inputs to be treated as the value of the ID variable that I set in the class. However, when I wrote this out, I was given an error. Could someone tell me what the issue is?
You should try to get your switch statement working correctly. To use classes setters, you can store the user input to a temporary variable then from your one student you can call the member function. i.e. in your case:
arr[index].setID(tempInputVariable);
There is no id in your main function or as a global variable.
I suggest you overload operator >> to have your structure extract its members from the data stream:
struct Student
{
//...
public:
friend std::istream& operator>>(std::istream& input, Student& s);
};
std::istream& operator>>(std::istream& input, Student& s)
{
input >> s.id;
input >> s.name;
input >> s.birthday;
return input;
}
Although the above code doesn't use setters, it is the preferred method for inputting data.
The overload can be modified to use setters (kind of overkill):
std::istream& operator>>(std::istream& input, Student& s)
{
int id;
input >> id;
s.setID(id);
std::string name;
input >> name;
s.setName(name);
int birthday;
input >> birthday;
s.setBirthday(birthday);
return input;
}
If you don't like the overload, you can perform the steps in your main function:
//...
Student new_student;
//...
{
int student_id;
std::cout << "Input Student ID:";
std::cin >> student_id;
new_student.setID(student_id);
std::string student_name;
std::cout << "Input Student Name: ";
std::cin >> student_name;
new_student.setName(student_name);
int student_birthday;
std::cout << "Input Student Birthday: ";
std::cin >> student_birthday;
new_student.setBirthday(student_birthday);
}
Edit 1: The Database
You'll probably need to store or remember the students. This is easy using the first method above:
std::vector<Student> database;
Student s;
std::cout << "Enter student information (ID, Name and birthday, separated by spaces:\n";
std::cin >> s;
// Append to the database
database.push_back(s);
If you haven't learned std::vector you can try an array:
const size_t MAXIMUM_STUDENTS = 16;
Student database[MAXIMUM_STUDENTS];
size_t database_index = 0;
//...
Student s;
std::cout << "Enter student information (ID, Name and birthday, separated by spaces:\n";
std::cin >> s;
// Append to database
database[database_index] = s;
++database_index;
Here is my code for an assignment I have. Whenever I try and compile I get an error for my read function due to something in "ios_base.h" I am not sure what to do and/or if my code does the intended function of taking a file and moving it's elements into a separate file that has the name and average next to each other.
#include <iostream>
#include <fstream>
#include <sstream>
#include <iomanip>
using namespace std;
struct Student
{
string fname;
string lname;
double average;
};
int read(ifstream, Student s[]);
void print(ofstream fout, Student s[], int amount);
int main()
{
const int size = 10;
ifstream fin;
ofstream fout;
string inputFile;
string outputFile;
Student s[size];
cout << "Enter input filename: ";
cin >> inputFile;
cout << "Enter output filename: ";
cin >> outputFile;
cout << endl;
fin.open(inputFile.c_str());
fout.open(outputFile.c_str());
read(fin , s);
print(fout, s, read(fin, s));
}
int read(ifstream fin, Student s[])
{
string line;
string firstName;
string lastName;
double score;
double total;
int i=0;
int totalStudents=0;
Student stu;
while(getline(fin, line)){
istringstream sin;
sin.str(line);
while(sin >> firstName >> lastName){
stu.fname = firstName;
stu.lname = lastName;
while(sin >> score){
total *= score;
i++;
}
stu.average = (total/i);
}
s[totalStudents]=stu;
totalStudents++;
}
return totalStudents;
}
void print(ofstream fout, Student s[], int amount)
{
ostringstream sout;
for(int i = 0; i<amount; i++)
{
sout << left << setw(20) << s[i].lname << ", " << s[i].fname;
fout << sout << setprecision(2) << fixed << "= " << s[i].average;
}
}
Stream objects are not copyable. Their copy constructor is deleted. They must be passed by reference, not by value:
int read(ifstream &, Student s[]);
void print(ofstream &fout, Student s[], int amount);
etc...
Sam Varshavchik's answer is correct, but he didn't mention why stream objects don't allow you to copy them.
The issue here is that a stream object owns a buffer, and buffers can't be copied safely.
To take an example, suppose you have data coming in over a network socket and a buffer sitting in front of it, and you copy this buffered reader. If you read from the copy, it will read some indeterminate amount of data and put it into the buffer. This data is now gone from the network socket and only exists in the buffer. Now suppose you read from the copy. Then you'll get some indeterminate amount of data that came after the data you read in the original. Going back and forth in this way, you'd get two "streams" with gaps in them where the other reader was reading the data.
I am new to vectors and new to classes.That being said, I have found some posts about how to create a vector of objects. I want to know how would one go about creating a vector of objects from user input? Say the program asks the user to give the number of employees(class) he/she wants to create. The user wants to add 5 employees. So user must input the employee's last name and first name. I have a for loop in mind but I am not sure how to go about grabbing the user input (Maybe using getline and push_back?) and storing it in the vector.
//Lets say class.h looks like this
class Employee
{
private:
string lastName;
string firstName;
public:
void setLastname(string);
void setFirstname(string);
string getLastname() const;
string getFirstname() const;
}
Your Employee class should have a constructor. When gathering input, you need all the constructor arguments. Then, to add an Employee to a vector<Employee>, call employees.emplace_back( ctor-arguments ).
std::vector has a nice method called emplace_back, which
Appends a new element to the end of the container. The element is constructed through std::allocator_traits::construct, which typically uses placement-new to construct the element in-place at the location provided by the container.
So the only thing you are missing to be able to use it is an appropriate constructor.
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Employee
{
private:
string firstName;
string lastName;
public:
void setLastname(string);
void setFirstname(string);
string getLastname() const{return lastName;}
string getFirstname() const{return firstName;}
//create a constructor
Employee(string firstName, string lastName)
: firstName(firstName), lastName(lastName)
{}
};
int main()
{
vector<Employee> emp;
int count = 0;
cout << "Enter the amount of employees to add:" << endl;
cin >> count;
string firstName, lastName;
for(int i = 0; i < count; ++i)
{
cout << "Please enter the first and last names" << endl;
cin >> firstName;
cin >> lastName;
emp.emplace_back(firstName, lastName);
}
for(const Employee & e : emp)
{
cout << "Employee:" << endl;
cout << e.getFirstname() << " " << e.getLastname() << endl;
}
}
Other users have provided a good examples explaining how to use emplace_back in modern C++.
If you work with pre-C++11 versions, there is no emplace_back method. In this case, you can collect data in your vector manually using old-style push_back. You can simply define a vector:
vector<Employee> employees;
Then, you can read your data line by line, create new objects, fill them according to your business logics and append to your vector:
int n;
int main()
{
cout << "Enter number of employyes: "; cin >> n;
for (int i = 0; i < n; i++)
{
std::string s;
Employee employee; // Create object
cout << "Employee " << i << ". First name: "; cin >> s;
employee.setFirstname(s); // Fill object
cout << "Employee " << i << ". Last name: "; cin >> s;
employee.setLastname(s); // Keep filling it
cout << "Welcome, " << employee.getFirstname() << " " << employee.getLastname() << endl;
employees.push_back(employee); // Add to vector
}
}
You can also define a constructor taking both firstname and lastname as arguments to make it easier to work with.
class Employee
{
private:
string lastName;
string firstName;
public:
Employee(string paramLastName, string paramFirstName) : lastName(move(paramLastName)), firstName(move(paramFirstName)) {}
void setLastname(string);
void setFirstname(string);
string getLastname() const;
string getFirstname() const;
}
You need a constructor that takes two strings as input. Obviously you could do without this but this reduces verbosity.
Employee(string paramLastName, string paramFirstName) :
lastName(move(paramLastName)), firstName(move(paramFirstName)) {}
You will need to call it in this way.
vector<Employee> inp;
string tmp1, tmp2;
while(std::cin>>tmp1 >> tmp2) {
inp.emplace_back(tmp1, tmp2);
}
(This is assuming that you will compile with c++11 support)