Passing Class object to the same class method

Hi folks, I have written code to random access files in c++ . I got result without creating a method for write a record to the file. I have given the code snippet below.

Code:

---

#include<iostream>

#include<fstream>
#include<iomanip>
using namespace std;
class student
{
 int rollno,marks;
 char name[20];
 fstream fpointer;
 
 public:
    void show();
    void get();

   
};
void student::get()
{
 cout<<"Enter the name of student:";
 cin>>name;
 cout<<"Enter the roll no. of student:";
 cin>>rollno;
 cout<<"Enter the marks of student:";
 cin>>marks;
}
int main()
{
 student record;
 fstream file;
 file.open("student.txt",ios::in|ios::out|ios::binary|ios::app);
 char flag='y';
 int i=0;
 while(flag=='y'||flag=='Y')
 {
    record.get();
    file.seekp(i*sizeof(record), ios::beg);
    file.write((char*)&record,sizeof record);
    cout<<"Enter another record(Y/N)....";
    cin>>flag;
    i++;
 }
 //file.seekg(0);
 cout<<"Roll No.\tName\tMarks"<<endl;
 file.seekp(2*sizeof(record), ios::beg);
 while(file.read((char*)&record,sizeof record))
 {
    record.show();
 }
 file.close();
 return 0;
}
void student::show()
{
 cout<<rollno<<"\t\t"<<name<<"\t"<<marks<<endl;
}

---

But now i created a method inside the class to write and read the record. This is time i could not write and read successfully. What is the problem here. Please tell me.

Code:

---

#include<iostream>

#include<fstream>
#include<iomanip>
using namespace std;
class student
{
 int rollno,marks;
 char name[20];
 
 
 public:
    void show();
    void get();
    int write(const student &,fstream &,int);
    int read(const student &,fstream &,int);
};
void student::get()
{
 cout<<"Enter the name of student:";
 cin>>name;
 cout<<"Enter the roll no. of student:";
 cin>>rollno;
 cout<<"Enter the marks of student:";
 cin>>marks;
}
int student::write(const student &s,fstream &fp,int RecNum)
{
    if( fp.seekp(RecNum*sizeof(s), ios::beg) == 0 )
        if(fp.write((char*)&s,sizeof s))
            return 1;
    return 0;
}
int student::read(const student &s,fstream &fp,int RecNum)
{
    if( fp.seekg(RecNum*sizeof(s), ios::beg) == 0 )
        if(fp.read((char*)&s,sizeof s))
            return 1;
    return 0;
}
int main()
{
 student record;
 fstream file;
 file.open("student.txt",ios::in|ios::out|ios::binary|ios::app);
 char flag='y';
 int i=0;
 
    record.get();
    record.write(record,file,2);
   
   
 

 cout<<"Roll No.\tName\tMarks"<<endl;
 
 record.read(record,file,2);

 file.close();
 return 0;
}
void student::show()
{
 cout<<rollno<<"\t\t"<<name<<"\t"<<marks<<endl;
}

---

Live 45 should be somethng like

Code:

---

file.open("student.txt",ios::in|ios::out|ios::binary|ios::app);
 if( !file.is_open() ){
        //Handle error here
        __asm nop;
 }

---

Line 29: if( fp.seekp(RecNum*sizeof(s), ios::beg) == 0 )
This is not the correct way to check for errors.
try

Code:

---

        fp.seekp(RecNum*sizeof(s), ios::beg);
        if( fp.good() ){
        if(fp.write((char*)&s,sizeof s))
            return 1;
        }else{
                //Handle error here
        }
    return 0;

---

Your error checking of seekg is incorrect as well.

Instead of checking for success, check for errors. That way, you don't need huge nested if statements which Microsoft is so fond of.

Code:

---

fp.seekp(RecNum*sizeof(s), ios::beg);
if (!fp)
{
        // Handle error here
        return 0;
}
return (fp.write((char*)&s, sizeof(s)) > 0);

---

Code:

---

return (fp.write((char*)&s, sizeof(s)) > 0);

---

If that works, it's not what you want. write returns a reference to the stream.

It does not make sense to have member functions that take another instance of the same class and ignore the 'this' pointer.
Either make the method static or do it properly by removing the const student &s and using the 'this' pts instead.
You should also ideally do proper serialisation rather than dumping the binary of the object to file, before it bites you later.

Quote:

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Originally Posted by whiteflags

Code:

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return (fp.write((char*)&s, sizeof(s)) > 0);

---

If that works, it's not what you want. write returns a reference to the stream.

---

I guess that backfired, huh? I just made a quick re-write of that function.
Oh well, just learn the advice; don't copy my sloppy re-coding :p