Class help

[Martonx]

Hi Everyone,

 

I have a C++ program lesson, but i can't to do it. I have a binary file with structured datas.

I have to read the datas, and take into a class (structure array).

 

Here is my code:

#include <iostream>
#include <fstream>

using namespace std;

struct dolgozo
{
char nev[30];
unsigned int kor;
long int fizetes;
};

class dolgoszt
{
private: 
dolgozo *adatok;
int db;
public: 
dolgoszt(char nev[])
{
	int i=0;
	db=0;
	dolgozo r;
	ifstream zh;
	zh.open(nev);
	if (zh.fail()) {cout<<"Error when open the file";exit(1);}
	zh.read((char*) &r, sizeof(dolgozo));
	while (!zh.eof())						
	{
		db++;
	}
	adatok = new dolgozo[db];
	zh.beg;
	zh.read((char*) &r, sizeof(dolgozo));
	while (!zh.eof())						
	{
		adatok[i]=r;
		i++;
		zh.read((char*) &r, sizeof(dolgozo));
	}
	zh.close();
	}
~dolgoszt();

void kiir()
{
	cout<<adatok->nev<<"\t"<<adatok->fizetes<<"\t"<<adatok->kor<<endl;
}

};


int main()
{
char file[30]="c:\\dolgozo.dat";
dolgoszt d(file);
cin.get();
}

 

But i can't compile this, i have some fatal error:confused:

I think this part has the problem:

adatok = new dolgozo[db];
zh.beg;
zh.read((char*) &r, sizeof(dolgozo));
while (!zh.eof())						
{
adatok[i]=r;
i++;
zh.read((char*) &r, sizeof(dolgozo));
}

 

I attached the binary file. Please help me. I am new in C++, i can programming in Visual Basic, but it is very hard to learn C++ :eek:

dolgozo.zip

[cugone]

Nothing against your educational institution of choice, but they should have started you on C++ to begin with...and not classes/db programming.

 

Anyway, what's the text of the error it's throwing?

[Diesel]

Well, I'll tell you what I think, see if that helps...

 

First, the compile errors:

 

dolgoszt d(file);

 

What is the d? I don't think that's valid syntax in c++.

Should just be: dolgoszt(file);

 

 

and this one:

 

adatok = new dolgozo[db];

 

 

Im pretty sure, this line: dolgozo *adatok;

won't allow you to save multiple dolgozo structures into it. A pointer is a container for a certain size of object and you are defining a pointer to a memory space for 1 dolgozo object. In this case, you might as well use an array, since you instantiate it as an array (adatok = new dolgozo[db]; ).

 

So, the change would be "dolgozo *adatok;" to "dolgozo adatok[];".

 

 

 

And for the logic errors:

 

1. The dolgoszt function doesn't give any output on success, so I would assume you want to call the kiir function after the call to it in the main function.

 

 

2. I think that this is a never ending loop:

 

while (!zh.eof())

{

db++;

}

 

 

unless eof increments the file pointer....which I don't think it does.

 

From what I see, you are trying to get the number of dolgozo structures in the file...You need to move the line before the while loop (zh.read((char*) &r, sizeof(dolgozo)); ) into the loop, so that the end condition will be met.

 

That does seem very inefficient though, you might want to refactor that part.

[MrPaul]

Code mistakes

 

First, the compile errors:

 

dolgoszt d(file);

 

What is the d? I don't think that's valid syntax in c++.

Should just be: dolgoszt(file);

 

The syntax is valid C++. dolgoszt is a class and d is an instance of dolgoszt, and the parameter file is passed to the constructor.

 

and this one:

 

adatok = new dolgozo[db];

 

 

Im pretty sure, this line: dolgozo *adatok;

won't allow you to save multiple dolgozo structures into it. A pointer is a container for a certain size of object and you are defining a pointer to a memory space for 1 dolgozo object. In this case, you might as well use an array, since you instantiate it as an array (adatok = new dolgozo[db]; ).

 

So, the change would be "dolgozo *adatok;" to "dolgozo adatok[];".

 

Again, incorrect. Martonx has the correct syntax for declaring and initializing an array - although you may wish to implement a destructor so that the array can be deleted when you are finished with the object.

 

1. The dolgoszt function doesn't give any output on success, so I would assume you want to call the kiir function after the call to it in the main function.

 

dolgoszt is a class, not a function.

 

The rest of your post, about the never ending loop, is accurate.

 

Good luck :cool:

[Diesel]

Woops, yeh, didn't pick up that that was a class with a constructor.

 

So, MrPaul, where is the compiler error then?

[MrPaul]

ios::beg

 

So, MrPaul, where is the compiler error then?

 

Most likely this line:

 

zh.beg;

 

I believe what is intended is:

 

zh.seekg(0, ios::beg);

 

Good luck :cool: