Problem with retrieving data from file

[johnkravetzki]

Hello everyone,
I've written (VC++ 2008 Express Edition) a simple database operating on txt file, but i have problem with retrieving int objects from it. I hope i won't need to paste my whole code here, anyway i assume the rest is OK.

This is my class:

class Student
{
private:

char* Name;
char* Surname;
int Age;
.........etc
};

And those are functions for saving/loading data (from) file:

void SaveToFile(Student* student, int recordNumber)
{
fstream nfile("database.txt",ios::out);
for (int i=0; i<recordNumber; i++)
{
	nfile<<student[i].PrintName()<<endl;     
        //Printxxx() functions are returning Name/Surname/Age...
	nfile<<student[i].PrintSurname()<<endl;
	nfile<<student[i].PrintAge()<<endl;

}
nfile.close();
}

void LoadFromFile(Student* student, unsigned &Record)
{
int i = 0;
ifstream nfile("database.txt",ios::in);
if(nfile.good())
{
	while (!nfile.eof()) {
		nfile>>student[i].PrintName()<<endl;
	        nfile>>student[i].PrintSurname()<<endl;
	        nfile>>student[i].PrintAge()<<endl;  //(1)look below
		Record++;		
		i++;
	}
}else
	cout<<"Error while opening the file"<<endl;
nfile.close();
}

Ad. (1) - i always receive an error in this part:

error C2679: binary '>>' : no operator found which takes a right-hand operand of type 'int' (or there is no acceptable conversion)

Could not find any suitable info elsewhere, what i found were infos about streamstring and operator overload(but i ain't sure if that may help here).

Does anyone know how that part of code should look like?

Ad. 2 - If i throw away those 2 lines, responsible for saving/loading Age (that nasty integer) the program works fine, but always when i save the data and then after a while load it from the file i receive an extra empty field...
I'm not sure why it happens. In the begin i thought EOF is equal to "0" but that's not true... Any ideas?

I hope my poct wasn't that chaotic. I'm looking forward you will find a proper solution for me...
Thx in advance
John Kravetzki

[jloundy]

please use code [tags], it makes it a lot easier on us to read and you will get greater responses

[helios]

1. I'm assuming PrintAge() returns an int. The problem with the assignment is that you're trying to assign to a temporary value returned by PrintAge(), which is invalid. To change the least amount of code, you could make it return an int &, but this is basically the same as making Age public.

[johnkravetzki]

Ad. 2 - If i throw away those 2 lines, responsible for saving/loading Age (that nasty integer) the program works fine, but always when i save the data and then after a while load it from the file i receive an extra empty field...
I'm not sure why it happens. In the begin i thought EOF is equal to "0" but that's not true... Any ideas?

wow, what kind of noob i am :) I forgot what means <<endl :))))
here is my solution:

void SaveToFile(Student* student, int recordNumber)
{
fstream nfile("database.txt",ios::out);
for (int i=0; i<recordNumber; i++)
{
	nfile<<student[i].PrintName()<<endl;     
        //Printxxx() functions are returning Name/Surname/Age...
        if(i==(recordNumber-1)
        {
	       nfile<<student[i].PrintSurname();
        }else
               nfile<<student[i].PrintSurname()<<endl;

	//nfile<<student[i].PrintAge()<<endl;

}
nfile.close();
}

[Duthomhas]

nfile>>student[i].PrintAge()<<endl; //(1)look below
Don't use << or endl when performing input.

(Not unless, of course, you do something like I did here: http://www.cplusplus.com/forum/beginner/11402/page1.html#msg53942 , and define your own endl manipulator for input streams...)

[johnkravetzki]

i think i found the solution (and i was wrong, it is possible to overload the operator while having string/int variables in the class)
Here it is in complete (for other generations :P):

class Student
{
private:

std::string Name;
std::string Surname;
int Age;

public:

friend std::ostream& operator<<(std::ostream& nFile, Student& student);
friend std::istream& operator>>(std::istream& nFile, Student& student);
.....
etc

std::ostream& operator<<(std::ostream& nFile, Student& student)
{
	nFile.write(reinterpret_cast<char*>(&student.Age), sizeof(student.Age));
	nFile << student.Name << '\0';
	nFile << student.Surname << '\0';
	return nFile;
}
std::istream& operator>>(std::istream& nFile, Student& student)
{
	nFile.read(reinterpret_cast<char*>(&student.Age), sizeof(student.Age));
	std::getline(nFile, student.Name, '\0');
	std::getline(nFile, student.Surname, '\0');
	return nFile;
}

void SaveToFile(Student* student, int recordNumber)
{
std::fstream nfile("database.txt",std::ios::out);
for (int i=0; i<recordNumber; i++)
    nFile << student[i];
nFile.close();
}

void LoadFromFile(Student* student, unsigned &Record)
{
int i = 0;
std::fstream nfile("database.txt",std::ios::in);
if(nfile.good())
{
	while (nFile >> student[i]) {
		Record++;		
		i++;
	}
}else
	cout<<"Error while opening the file"<<endl;
nFile.close();
}