C++

Forum

 
Need help on reference parameter

ken2012 (10)
Hi guys,
I'm working on my second homework. It basically read in a text file of books list and determine which book is valid and which in invalid. Once I determined these lists, I need to print out the valid books, invalid call numbers, and update the book using another text file.
Here is my code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
 
#include "std_lib_facilities.h"
#include "Book.h"
#include <iostream>
#include <fstream>
#include <vector>
#include "BadCallNumException.h"
using namespace std;

void readInput(vector<Book>&Books);
void printBooks(vector<Book>&Books);
//void printInvalidCallNum(vector<Book>&Books);
//void processTrans(vector<Book>&Books);
//void searchBooks(vector<Book>&Books);

int main()
{	
	vector<Book> Books;
	readInput(Books);
	printBooks(Books);

	//printInvalidCallNum(Books);
	//processTrans(Books);
	//searchBooks(Books);
	
	
	keep_window_open();
	return 0;
}

void readInput(vector<Book> &Books)
{
	string callNum;
	string title;
	string author;
	int date;
	ifstream fin ("input2.txt");
	if (!fin)
		cout<<"Cannot open input file"<<endl;

	while(fin>>callNum>>title>>author>>date)
	{
	
			Book List(callNum, title, author, date);
				List.setCallNum(callNum);
				List.setTitle(title);
				List.setAuthor(author);
				List.setDate(date);
				Books.push_back(List);
	}
	fin.close();
} 
//Print out valid book;
void printBooks(vector<Book>&Books)
{
	
	Book List;
	string cNum;
	if(!List.setValid(cNum))
	{
		vector<Book> errorBooks;
		errorBooks.push_back(List);
		for (int i=0; i<errorBooks.size(); i++)
		{ 
			cout<<errorBooks[i]<<endl;
		}
	}
} 
void printInvalidCallNum(vector<Book>&Books)
{}
void processTrans(vector<Book>&Books)
{}
void searchBooks(vector<Book>&Books)
{}


for the printBooks function, how do I print out using reference paramater? I have trouble understanding the concept :( Any help would be appreciated.
btw...I also have book.cpp and book.h
and here is an example of a string inside the text file

QA76.1 Mindstorms Seymour_Pappert 1980
Q76.2 Karel_the_Robot Rich_Pattis 1992 //error
QA76.3 Programming Byarne_Stroustrup 2011
72QA.4 Error_Book No_Name 2012 //error
QA76.5 A_C.S._Tapestry Owen_Astrachan 1990
QA76.7 I_Was_Right_On_Time Buck_O'Neill 1955
QA768 Principles_of_Parallel_Programming Calvin_Lin 2009 //error
QAo55.6 Embedded_Software Daniel_Lewis 2011 //error
QA76.7.1 Core_Java_I Cay_Horstman 2005
QA76.7.2 Core_Java_II Cay_Horstman 2006


The call numbers will always be two letters followed by a series of digits and at least one decimal point so there are total of 4 error books
Vortex47 (11)
Can't you just use ofstream to print out Books? Or whatever you wanted to print out. Or am I just stupid?
therockon7throw (284)
Hi

the function printBooks is expected to print out the books using the reference, first the param which the function takes should be a kind of const.
Second why should the prinBooks function call setValid, and why should setValid return a boolean ? and what is the value of cNum which you are provding the setValid function ?

you are just doing all others than printing the data out :-)


If you arr tring to print out valid or invalid Books, so you should have some method in Books which tell you whether a Book is valid or not, e.g getValid , and not setValid( setValid is to set whether a Book is valid or not )

a begin point for you may be as following


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
 
void printBooks(const vector<Book>& Books)
{
	

	for( unsigned int i = 0 ; i < Books.size() ; i++ ){
            if(!Books[i].getValid() )
	  {
		//do whatever you wish for invalid books
		
	  }
           else{
            // do whatever you wish for valid books
           }
     }
}


hope it helps
Last edited on
ken2012 (10)
@Vortex47: Yes, I will need to use ofstream to print the list into a text file but first i need to determine which book is valid and error books. I use cout so I dont have to open the text file every time I run the program


@therockon7thow: I have setValid because in my book.cpp file, I have a private function called getValid. In order to access to that function i have to create a void setValid function in public so I can use it in main.cpp

btw...thanks for the help I will try to work on it
ken2012 (10)
Here is my book.cpp and book.h file
I've changed the name of setValid to Valid in book class

Book.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
 
#pragma once
#include <string>
using namespace std;
class Book
{
public:
	Book(void);
	Book(string callNum, string title, string author, int date);
	~Book(void);
	string getCallNum();
	string getTitle();
	string getAuthor();
	int getDate();
	void setCallNum(string callNum);
	void setTitle(string title);
	void setAuthor(string author);
	void setDate( int date);
	bool Valid(string cNum);


	friend ostream& operator <<(ostream &out, Book &cBook); 
	friend bool operator ==(const Book&, const Book&);
	friend bool operator != (const Book&, const Book&) ;
private:
	string callNumber;
	string Title;
	string Author;
	int copyrightDate;
	bool isValid(string callNum);
	
};


Book.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
 
#include "Book.h"
#include <iostream>
using namespace std;

Book::Book(void){
}
Book::~Book(void){
}
Book::Book(string callNum, string title, string author, int date): 
callNumber(callNum), Title(title), Author(author) , copyrightDate(date)
{
}
string Book::getCallNum()
{
	return callNumber;
}
void Book::setCallNum(string callNum)
{
	callNumber=callNum;
}
string Book::getTitle()
{
	return Title;
}
void Book::setTitle(string title)
{
	Title = title;
}
string Book::getAuthor()
{
	return Author;
}
void Book::setAuthor( string author)
{
	author=Author;
}
int Book::getDate()
{
	return copyrightDate;
}
void Book::setDate( int date)
{
	copyrightDate = date;
}

bool Book::isValid(string cNum)
{

	if (!isalpha(cNum.at(0)))
		return false;
	else if (!isalpha(cNum.at(1)))
		return false;
	else if (isalpha(cNum.at(2)))
		return false;
	else if (isdigit(cNum.at(4)))
		return false;
	else
		return true;
}
bool Book::Valid(string cNum)
{
	return isValid(cNum);

}
therockon7throw (284)
remove the Valid method and make the isValid a public method, and make your method simple, e.g. some thing like


1
2
3
4
5
6
 
bool Book::isValid()
{
     if (!isalpha(callNumber.at(0) ) || !isalpha(callNumber.at(1) ) || isalpha(callNumber.at(2)) || isdigit(callNumber.at(4)) )
          return false;
   return true;
}



and modify your printBooks or your overloaded operator<< in a way that just call isValid for each Books to be printed or edited.

hope it helps
Last edited on
ken2012 (10)
Yes, that would be simpler but my instructor wanted the isValid function as a private function. :(

and one more question how do I use overloaded operator? do I use it inside main.cpp? or in the book.cpp sorry i have trouble understanding these
therockon7throw (284)

@ken2012 who wrote
and one more question how do I use overloaded operator? do I use it inside main.cpp? or in the book.cpp sorry i have trouble understanding these


Once you implement the overloaded operator( <<, == , != ) some where in a source file, than you can use them everywhere with object of your class , for example

in your main you may have some thing like following ;

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
 

int main(int argc, char* argv[]){

        vector<Book> Books;
	readInput(Books);
	printBooks(Books);

	// a dummy example
      for(unsigned int i = 0 ; i < Books.size() - 1; i++)
      {
            // use == operator 
            if( Books[i] == Books[ i + 1 ] ){
                //do some dummy things :-)
             }
              if(Books[i] != Books[ i + 1 ]){
                  // do some other dummy things :-)
                 // you may print the current object out using your overloaded operator <<
                 cout<< Books[i] << endl;
             }
      }
  
  return 0;
}



hope it helps
ken2012 (10)
:) ok...that answered my question. nice explaination and very helpful. Your example is way better than the example in the book lol
Thanks a lot :)

Topic archived. No new replies allowed.