I want to store the contents of a .txt file as attributes of different objects which I can then store in a vector. Is there a simple way to do this.
My txt file looks like this:
a0 0 4 0 10
a1 0 3 0 20
a2 0 2 0 30
I tried to do it like this but i get an error.
class process {
public:
std::string name;
int arrivalTime;
int priority;
int age;
int ticketsReq;
int time;
process(std::string name, int arrivalTime, int priority, int age, int ticketsReq) {
this->name = name;
this->arrivalTime = arrivalTime;
this->priority = priority;
this->age = age;
this->ticketsReq = ticketsReq;
this->time = 0;
}
};
int main() {
std::ifstream theFile("input.txt");
int i = 0;
std::vector<process> a;
std::string nameT;
int arrivalTimeT;
int priorityT;
int ageT;
int ticketsReqT;
int timeT;
while(theFile>>nameT>>arrivalTimeT>>priorityT>>ageT>>ticketsReqT){
a[i] = process (nameT,arrivalTimeT,priorityT,ageT,ticketsReqT);
i++;
}
}
Okay, I see at least one problem.
First, vector assumes you call push_back to add elements to the vector. You can do vector[index] to access an element once it exists. But you're going to get a range problem with that.
Second, this line doesn't make sense:
a[i] = process (nameT,arrivalTimeT,priorityT,ageT,ticketsReqT);
At the point you do this, you don't have a "this" for process. You would need to do something like:
process myObj(nameT,arrivalTimeT,priorityT,ageT,ticketsReqT);
a.push_back(myObj);
As a side-point, I personally never store objects in std::vector. I store pointers to objects. I don't know if someone else can comment on this, but consider what happens. You may want to write a simpler example to test that.
Related
I'm having trouble with one of my assignments (or maybe I'm overthinking it?)
I need to create
a function to take integer parameters for number of students and tests.
Allocate the memory needed for the array of students and the array of test scores for each student.
Return a pointer to the array of Student structures. No display output is done in this function.
int main()
{
int studentNum;
int testNum;
cout << "How many students are there?\n";
cin >> studentNum;
cout << "How many tests are there?";
cin >> testNum;
system("pause");
return 0;
}
my function
GradeBook *initArrays(int s, int t)
{
GradeBook *ptr;
// Allocate the array of Student structures.
ptr = new GradeBook[s];
// Allocate an array of ints (to hold test scores)
// for each element of the array of Student structures.
for (int count = 0; count < s; count++)
{
ptr[count].tests = new int[t];
}
// Return a pointer to the array of structures.
return ptr;
}
edit: I have edited my function, could i get some opinions on that?
if you are writing this in c++, use classes. if i understand correctly, you should create a structure to save a students id,name,or something and a corresponding grade?
something like:
class Test{
public:
int id;
int grade;
Test(int id, int grade){
this->id = id;
this->grade = grade;
}
};
class Student{
public:
int id;
std::string name;
std::vector<Test> tests;
Student(int id, std::string name)
{
this->id = id;
this->name = name;
}
};
int main(){
vector<Student> students;
int studentnum;
for (int i = 0; i < studentnum; i++){
students.push_back(Student(i, "name"));
//insert all tests of the student by calling students[i].tests.push_back(Test(id, grade))
}
}
this way you don't have to allocate memory, which you can easily overlook freeing.
edit:
this is very basic and not a sophisticated solution, as the properties of the classes are all public.
edit 2:
typedef struct Test{
int id;
int grade;
}Test;
typedef struct Student{
int id;
std::string name;
Test * tests;
}Student;
int main(){
Student * students;
int studentnum;
students = (Student*)malloc(sizeof(Student)*studentnum);
for (int i = 0; i < studentnum; i++){
students[i]->id = id;
students[i]->name = "name";
student[i]->tests = (Test*)malloc(sizeof(Test)*numberofgradesofthatstudent);
for (int j = 0; j < numberofgradesofthatstudent; j++)
{
students[i]->tests[j]->id = testid;
students[i]->tests[j]->grade = grade;
}
}
}
this is schematic! new and malloc reserve memory on the heap, do not forget to free everything when you are done with it.
As said a little above, be careful using brackets {} to delimit your blocks.
Secondly,the syntax:
array[studIndex].Tests
supposes that the value array[studIndex] (here an integer) has a member value named Tests. But in this case it doesn't.
Think about your problem: you need to store two values "connected" to one another in a static array. The way I see it, you should try on with two dimensional arrays:
int 2dArray[nbStudents][nbTests];
If you don't want to bother with 2dimensional arrays, you can also try
int 2dArray[nbStudents * nbTests];
But for conveniance, it is often better to use 2d arrays.
Also, think about declaring your array before the for loops in your function.
Then concatenate two for loops as you did and I'll let you think about the rest...
#include <iostream>
#include <string.h>
#include <time.h>
using namespace std;
struct MyID
{
char FirstName[10]; // array for lenight of the word.
char LastName[10]; // array for lenight of the word.
int IdNumber;
};
void InitializeArray(MyID IDNumber[], int Size);
//void SortTheArray(MyID IDNumber[], int Size);
int main(){
const int Size = 100;
MyID IDNumber[Size];
strcpy_s(IDNumber[Size].FirstName, "Aziz");
strcpy_s(IDNumber[Size].LastName, "LEGEND");
// I believe the error is around here.
InitializeArray(IDNumber, Size);
//SortTheArray(IDNumber, Size);
}
void InitializeArray(MyID IDNumber[], int Size){
//srand(time(0));
for (int i = 0; i < Size; i++){
//IDNumber[i].IdNumber = rand() %100 ;
cout<<IDNumber[i].FirstName<<endl;
IDNumber[i].LastName;
}
}
I have this problem, every time I want to test my function and struct, this error will prompt. Also, I want to see if my name will print correctly before continue to write rest program. The idea is I want to print same name every time without ask user to print name every time.
Also, I have upload the picture of result if you want to see it.
Because you are using arrays, you are experiencing buffer overrun error:
const int Size = 100;
MyID IDNumber[Size];
strcpy_s(IDNumber[Size].FirstName, "Aziz");
strcpy_s(IDNumber[Size].LastName, "LEGEND");
The expression IDNumber[Size] is equivalent to IDNumber[100].
In C++, array slot indices go from 0 to Size - 1. You are accessing one past the end of the array.
Edit 1: Initializing an array
Based on your comment, you can use a loop to initialize the slots in an array (vector):
struct Person
{
std::string first_name;
std::string last_name;
};
const unsigned int CAPACITY = 100;
int main()
{
std::vector<Person> database(CAPACITY);
Person p;
std::ostringstream name_stream;
for (unsigned int i = 0; i < CAPACITY; ++i)
{
name_stream << "Aziz" << i;
database[i].first_name = name_stream.str();
database[i].last_name = "LEGEND";
}
return 0;
}
So I've to do another exercise. This time I need to define a struct and a 100-elements array, which will store information about the book (title, author, ID number, price) and a simple function which will print info about all of the books stored. I started with that code:
#include <iostream>
using namespace std;
int main()
{
struct name_surname {string name, surname;};
struct book {string title; name_surname author_name, author_surname; int ID; int price;};
return 0;
}
And, well, what now? How can I store this in an array?
You just create an array of type book or name_surname or whatever you want.
Example:
book arr[100];
arr[0].title = "The last robot";
arr[0].ID = 2753;
Tips:
It's good programming practice if your structs/classes begin with with capital letter, so it's easier to distinguish them and so it is easier to name the variable the same name just without the capital letter. Example.
struct Name_surname
{
string name, surname;
};
Name_surname name_surname[100];
name_surname[0].name = "MyName";
Another tip is that I'd really suggest you learn how to research, this question has been answered millions of times and answers are all over the internet.
Here is my suggestion :
struct book
{
string title;
string name_surname;
string author_name;
string author_surname;
int ID;
int price;
};
struct Database
{
book *array;
void printDatabase()
{
for(int i = 0 ; i < 100 ;i++)
cout<<array[i].title<<endl;
}
Database()
{
array = new string [100];
}
};
Your name structure seems a little confused but creating an array is simply a case of declaring a variable with [] appended to it giving the size.
For example:
struct full_name
{
std::string firstname;
std::string surname;
};
struct book
{
std::string title;
full_name author;
int ID;
int price;
};
int main()
{
// Declare an array using []
book books[100]; // 100 book objects
// access elements of the array using [n]
// where n = 0 - 99
books[0].ID = 1;
books[0].title = "Learn To Program In 21 years";
books[0].author.firstname = "Idont";
books[0].author.surname = "Getoutalot";
}
What do you think about that:
#include <iostream>
using namespace std;
struct book {string title; string name; int ID; int price;} tab[100];
void input(book[]);
void print(book[]);
int main()
{
input(tab);
print (tab);
return 0;
}
void input(book tab[])
{
for (int i=0;i<3;i++)
{
cout<<"\nBook number: "<<i+1<<endl;
cout<<"title: ";cin>>tab[i].title;
cout<<"name: ";cin>>tab[i].name;
cout<<"ID: ";cin>>tab[i].ID;
cout<<"price: ";cin>>tab[i].price;
}
}
void print (book tab[])
{
for (int i=0; i<3; i++)
{
cout<<"\nBook number: "<<i+1<<endl;
cout<<"title: "<<tab[i].title;
cout<<"\nname: "<<tab[i].name;
cout<<"\nID: "<<tab[i].ID;
cout<<"\nprice: \n"<<tab[i].price;
}
}
I've done this with help from some Yt video. It works, but, is there a way to do it better, or just leave it how it is? And I have a question: Why those function parameters? Can't I just say tab[] or something else?
Computer languages are based on general and recursive rules. Just try to experiment and extrapolate with the basic understanding to build seemingly complex stuff. Coming to what you are trying to achieve:
We know, an array can be declared for any data-type (primitive or derived, one might call them POD and ADT).
We know, struct can comprise of any number of elements of any data-types.
Now, we can see that it is just as natural to say MyStruct[] as it is to int[].
It is better to prefer std::array if using modern compiler.
I have a class named Student
class Student
{ string name;
unsigned long int ID ;
string email;
unsigned short int year;
public :
Student() // Constructor
string getName(void);
unsigned long int getID(void);
string getEmail(void);
unsigned short int getYear(void);
{
and another class named eClass
class eClass {
private:
string eclass_name;
Student* students[100];
unsigned int student_count;
public:
eClass(string name)
{
student_count =0 ;
eclass_name = name ;
}
bool exists(Student obj)
{
unsigned long int code = obj.getID();
bool flag = TRUE ;
for (unsigned int i = 0 ; i<=student_count ; i++ )
{
unsigned long int st = (*students[i]).getID();
if (code==st)
{
flag = FALSE;
}
}
return flag;
}
void add(Student& obj)
{
bool res = exists(obj);
if (res)
{
students[student_count] = new Student(); //probably the problem is here
*students[student_count] = obj ;
student_count++ ;
}
}
string getEclassName(void) { return eclass_name; }
unsigned int getStudentCount(void) { return student_count; }
Student getStudent(int i) { return *students[i-1]; }
};
The statement Student* students[100]; must look exactly like this . For example I can't write something like this: Student* students[100]={} ;
And main() looks like this
int main()
{
Student JohnDoe("John Doe", 12345, 2, "johndoe#gmail.gr");
eClass Cpp("C++");
Cpp.add(JohnDoe);
}
Basically I have an array of pointers to Student objects and I want to allocate dynamically memory every time I want to add a new Student object.
When I compile I get no errors but when I try to run the program the only thing I get is "Program_name.exe" stopped running...
I'm pretty sure the problem has to do with memory allocation but I'm not able to find it and solve it.
Any suggestions ?
The main bug in exists was the loop went one too far, using an uninitialized pointer. But also it is very bad style for exists to take its input by value. Fixing both of those:
bool exists(Student const& obj)
{
unsigned long int code = obj.getID();
bool flag = TRUE ;
for (unsigned int i = 0 ; i<student_count ; i++ )
{
unsigned long int st = (*students[i]).getID();
if (code==st)
{
flag = FALSE;
}
}
return flag;
}
You should declare getID() const inside student in order to be able to code exists correctly.
unsigned long int getID() const;
First, you should initialize all of your student pointers to either NULL or nullprt. This is not strictly needed but is a very good habit to get into. You'll thank yourself later.
Second, why are you returning false if the student exists? Kind of confusing I'd imagine. Also, you can use the break statement after you find your student exists; no need to check the rest of them.
Also, on your add, you may want to check to ensure you don't have MORE than 100 students. This will overwrite memory and bad things will happen.
I am struggeling with reading from a binary file.
My binary file is made of records in the way like:
string - 5 x integers
The first string has differenct lengths, so I guess this may be my problem?
I try to read a record into a class which has the same type of attributes:
class Team
{
private:
string teamName;
int matchesPlayed;
int gamesWon;
int gamesLost;
int pointsWon;
int pointsLost;
public:
Team(string ="",int = 0,int = 0, int = 0, int = 0, int = 0);
~Team();
//void operator<();
void setTeamName(string);
void setMatchesPlayed(int);
void setGamesWon(int);
void setGamesLost(int);
void setPointsLost(int);
void setPointsWon(int);
void print();
};
I try to read in from another class:
Table::Table()
{
Team t1;
teams.push_back(t1);
ifstream inputFile;
inputFile.open("tabletennis.dta", ios::in | ios::binary);
if(!inputFile)
{
cout << "Datei konnte nicht geoeffnet werden!";
exit(1);
}
if(inputFile.good())
inputFile.read(reinterpret_cast<char*> (&t1), sizeof(Team));
t1.print();
}
Team::print() just prints out the content of its attributes. But the program crashes when I try to print the string.
I don't know what I may understood wrong.. but what I thought was:
Reading in to an Object with the same count and type of attributes is they way how to read a record set:
Team::Team(string teamName, int matchesPlayed, int gamesWon, int gamesLost, int pointsWon, int pointsLost)
{
setTeamName(teamName);
setMatchesPlayed(matchesPlayed);
setGamesWon(gamesWon);
setGamesLost(gamesLost);
setPointsWon(pointsWon);
setPointsLost(pointsLost);
}
Don't know for now..
Yep, if you want to do record-based I/O, then the records must really all have the same length. and record-based I/O is a rare occasion when using an array of char may be a better bet than a std::string. I would change this:
class Team
{
private:
string teamName;
int matchesPlayed;
int gamesWon;
int gamesLost;
int pointsWon;
int pointsLost;
to:
class Team
{
private:
char teamName[NAMESIZE];
int matchesPlayed;
int gamesWon;
int gamesLost;
int pointsWon;
int pointsLost;
You can then read and write:
Team t( .... ); // construct a team
os.write( (const char *) & t, sizeof( t ) );
and read:
Team t; // default construct empty team
is.read( (char *) & t, sizeof( t ) );
Nothing more to add to the answer of Neil but
I would suggest that you take a look at boost serialization.
If your file format is not fixed and you can easily change it, this will really help you to avoid a lot of traps in serialization.