Programming Forums > Application Development > C++

Dan · Sep 20th, 2005, 1:59 PM

My previous post didn't post for some reason, I'll try again

The code below does the following - A Class named My_class has a function that asks to enter names until 'n' is entered. The names are saved to a file. The file is opened again and all the names saved in the file are printed to the screen.

The problem is only the last name entered is printed to the screen when I use Dev c++, why is this? The program doesn't even run in Visual C++

How do I get all the names to print to screen and what am I doing wrong? Hope you can help

#include <conio.h>
#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

class My_class
{
private:
char name[20];

public:
void enternames();
void printnames();
};

void My_class::enternames()
{
cout<<"\nEnter a name : ";
gets(name);
}

void My_class::printnames()
{
cout<<"\nName = "<<name;
}

int main(void)
{
fstream namefile;

My_class X;

namefile.open("myfile.dat",ios::out);

do{
X.enternames();
namefile.write((char*)&X,sizeof(My_class));
cout<<"\nWould you like to enter another name? y/n ";
}while(getch()!='n');
namefile.close();

namefile.open("myfile.dat",ios::in);

while(namefile.read((char*)&X,sizeof(My_class)));
{
X.printnames();
}
namefile.close();

getch();
return 0;
}

Dan · Sep 20th, 2005, 2:01 PM

I don't know what's up with the smiley faces in the code... sorry

stevengs · Sep 20th, 2005, 2:08 PM

Quickly hit the 'edit' button under your post, and put code tags around your code. There is a code-tags icon at the top of your editor window. It will retain formatting (spaces/tabs) which makes your code MUCH easier to read. (you can use the PHP tags if you want color highlighting as well

)

you can only edit your post 30 minutes, after which it will be locked.

What are the contents of the file? Were all the names concatenated, or is only the last name present?

* a wild guess, maybe you should use ios :: app?

iignotus · Sep 20th, 2005, 2:09 PM

You must use code tags. It's in the rules, no less.

Dan · Sep 20th, 2005, 2:33 PM

My previous post didn't post for some reason, I'll try again

The code below does the following - A Class named My_class has a function that asks to enter names until 'n' is entered. The names are saved to a file. The file is opened again and all the names saved in the file are printed to the screen.

The problem is only the last name entered is printed to the screen when I use Dev c++, why is this? The program doesn't even run in Visual C++

How do I get all the names to print to screen and what am I doing wrong? Hope you can help

(Toggle Plain Text)

#include <conio.h>
#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

class My_class
{
      private:
      char name[20];
      
      public:
      void enternames();
      void printnames();
};

void My_class::enternames()
{
     cout<<"\nEnter a name : ";
     gets(name);
}

void My_class::printnames()
{
     cout<<"\nName = "<<name;
}

int main(void)
{
    fstream namefile;
    
    My_class X;  
    
    namefile.open("myfile.dat",ios::out);
    
    do{
       X.enternames();
       namefile.write((char*)&X,sizeof(My_class));
       cout<<"\nWould you like to enter another name? y/n ";
       }while(getch()!='n');
    namefile.close();
    
    namefile.open("myfile.dat",ios::in);
    
    while(namefile.read((char*)&X,sizeof(My_class)));
    {
     X.printnames();
    }
    namefile.close();
    
    getch();
    return 0;
}

Sorry about the tags guys, hope this works... I'd just like to see all the names I entered during each "run" It doesnt matter what happens to the file after I close.....sorry, I'm not familiar with the correct terms.

Infinite Recursion · Sep 20th, 2005, 2:43 PM

You may want to change OUT to APP... otherwise, you are overwriting your file.

(Toggle Plain Text)

namefile.open("myfile.dat",ios::out);

call this function to read the file after all of your names are entered:

(Toggle Plain Text)

void ReadFile (void)
{
ifile.open("myfile.dat");
string x;
 
while(ifile >> x)
	 {
		cout << x;
		cout << endl;
	 }
	 ifile.close();
}

Infinite Recursion · Sep 20th, 2005, 3:25 PM

Disregard my code above...

Keep in mind that using OUT on your data file, will overwrite anything that's in it each time the file is opened for output. You will need to use APP to append data in cases like this.

Here's how I would have went about it... you will need to turn it into OOP, etc.

(Toggle Plain Text)

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
 
using namespace std;
 
void WriteToFile (string data);
void ReadFile (void);
ofstream ofile;
ifstream ifile;
 
int main (void)
{
char name[256];
 
while (strcmp(name,"n") != 0)
{
cout << "Enter name: ";
cin.getline(name,200,'\n');
if (strlen(name) > 2)
WriteToFile (name);
}
 
 
ReadFile();
system("PAUSE");
 
return 0;
}
 
void WriteToFile (string data)
{
ofile.open("myfile.dat",ios::app);		//open a file
	ofile << data << endl;	//write to it
	ofile.close();				//close it
}
 
void ReadFile (void)
{
char ch;
ifile.open("myfile.dat");
 
while(!ifile.eof())
	 {
char temp[256];
		ifile.getline(temp,256);
		cout << temp << endl;
	 }
}

DaWei · Sep 20th, 2005, 3:26 PM

If you use ios::app, be sure and use ios::binary, too, or it won't work as you expect.

Dan · Sep 20th, 2005, 7:46 PM

I'm stumped but first thanks to all of you for taking the time to reply.

Infinite recursion, a special thanks for writing out the code for me...your's worked like a charm and I'm going to save it.

Following DaWei and your example I tossed the ios::out and added ios::binary and ios::app. My program still doesn't print out all of the names, only the last one entered.

Sorry for being so insistant with getting my version to work but it's the format we're commenting with in class so I'd like to get it to work and understand why. Would it be possible to modify it only slightly and have it to work?

..here's the new code with app and binary....same result as before.

(Toggle Plain Text)

#include <conio.h>
#include <iostream.h>
#include <fstream.h>
#include <stdio.h>

class My_class
{
      private:
      char name[20];
      
      public:
      void enternames();
      void printnames();
};

void My_class::enternames()
{
     cout<<"\nEnter a name : ";
     cin>>name;
}

void My_class::printnames()
{
     cout<<"\nName = "<<name;
     cout<<flush;
}

int main(void)
{
    fstream namefile;
    
    My_class X;  
    
    namefile.open("myfile.dat",ios::binary|ios::app);
    
    do{
       X.enternames();
       namefile.write((char*)&X,sizeof(My_class));
       cout<<"\nWould you like to enter another name? y/n ";
       }while(getch()!='n');
    namefile.close();
    
    namefile.open("myfile.dat",ios::binary|ios::in);
    
    namefile.seekg(0);
    while(namefile.read((char*)&X,sizeof(My_class)));
    {
     X.printnames();
    }
    namefile.close();
    
    getch();
    return 0;
}

Scorpions4ever · Sep 20th, 2005, 8:14 PM

This is why you should always put some error checking in your code. If you'd checked namefile.good() after the first namefile.open(), you would have realized that the file wasn't opened for write properly at all. You really need to open it with:

(Toggle Plain Text)

namefile.open("myfile.dat",ios::binary|ios::app|ios::out);
if (!namefile.good()) {
   cerr << "Open failed" << endl;
   return -1;
}

Note the extra ios parameter I added. If you don't have it, your open() will fail.
With that said, you haven't handled reading it back correctly either. Here's how to really do it:

(Toggle Plain Text)

#include <iostream>
#include <fstream>
#include <cstdio>
using namespace std;

class My_class
{
      private:
      char name[20];

      public:
      void enternames();
      void printnames();
};

void My_class::enternames()
{
     cout<<"\nEnter a name : ";
     cin>>name;
}

void My_class::printnames()
{
     cout<<"\nName = "<<name;
     cout<<flush;
}

int main(void)
{
    fstream namefile;

    My_class X;

    namefile.open("myfile.dat",ios::binary|ios::app|ios::out);
    if (!namefile.good()) {
      cerr << "Open failed" << endl;
      return -1;
    }

    do{
       X.enternames();
       namefile.write((char*)&X,sizeof(My_class));
       cin.ignore(1);
       cout<<"\nWould you like to enter another name? y/n ";
       }while(getchar()!='n');
    namefile.close();

    namefile.open("myfile.dat",ios::binary|ios::in);
    if (!namefile.good()) {
      cerr << "Open failed" << endl;
      return -1;
    }

    namefile.seekg(0);
    while(!namefile.eof())
    {
      namefile.read((char*)&X,sizeof(My_class));
     X.printnames();
    }
    namefile.close();

    getchar();
    return 0;
}

Sep 20th, 2005, 1:59 PM	#1
Dan Newbie Join Date: Sep 2005 Posts: 7 Rep Power: 0	File stream problems My previous post didn't post for some reason, I'll try again The code below does the following - A Class named My_class has a function that asks to enter names until 'n' is entered. The names are saved to a file. The file is opened again and all the names saved in the file are printed to the screen. The problem is only the last name entered is printed to the screen when I use Dev c++, why is this? The program doesn't even run in Visual C++ How do I get all the names to print to screen and what am I doing wrong? Hope you can help #include <conio.h> #include <iostream.h> #include <fstream.h> #include <stdio.h> class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; gets(name); } void My_class::printnames() { cout<<"\nName = "<<name; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::out); do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cout<<"\nWould you like to enter another name? y/n "; }while(getch()!='n'); namefile.close(); namefile.open("myfile.dat",ios::in); while(namefile.read((char)&X,sizeof(My_class))); { X.printnames(); } namefile.close(); getch(); return 0; }

Sep 20th, 2005, 2:08 PM	#3
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	Quickly hit the 'edit' button under your post, and put code tags around your code. There is a code-tags icon at the top of your editor window. It will retain formatting (spaces/tabs) which makes your code MUCH easier to read. (you can use the PHP tags if you want color highlighting as well ) you can only edit your post 30 minutes, after which it will be locked. What are the contents of the file? Were all the names concatenated, or is only the last name present? * a wild guess, maybe you should use ios :: app? __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty Last edited by stevengs; Sep 20th, 2005 at 2:31 PM.

Sep 20th, 2005, 2:33 PM	#5
Dan Newbie Join Date: Sep 2005 Posts: 7 Rep Power: 0	My previous post didn't post for some reason, I'll try again The code below does the following - A Class named My_class has a function that asks to enter names until 'n' is entered. The names are saved to a file. The file is opened again and all the names saved in the file are printed to the screen. The problem is only the last name entered is printed to the screen when I use Dev c++, why is this? The program doesn't even run in Visual C++ How do I get all the names to print to screen and what am I doing wrong? Hope you can help (Toggle Plain Text) #include <conio.h> #include <iostream.h> #include <fstream.h> #include <stdio.h> class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; gets(name); } void My_class::printnames() { cout<<"\nName = "<<name; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::out); do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cout<<"\nWould you like to enter another name? y/n "; }while(getch()!='n'); namefile.close(); namefile.open("myfile.dat",ios::in); while(namefile.read((char)&X,sizeof(My_class))); { X.printnames(); } namefile.close(); getch(); return 0; } #include <conio.h> #include <iostream.h> #include <fstream.h> #include <stdio.h> class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; gets(name); } void My_class::printnames() { cout<<"\nName = "<<name; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::out); do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cout<<"\nWould you like to enter another name? y/n "; }while(getch()!='n'); namefile.close(); namefile.open("myfile.dat",ios::in); while(namefile.read((char)&X,sizeof(My_class))); { X.printnames(); } namefile.close(); getch(); return 0; } Sorry about the tags guys, hope this works... I'd just like to see all the names I entered during each "run" It doesnt matter what happens to the file after I close.....sorry, I'm not familiar with the correct terms.

Sep 20th, 2005, 2:43 PM	#6
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	You may want to change OUT to APP... otherwise, you are overwriting your file. (Toggle Plain Text) namefile.open("myfile.dat",ios::out); namefile.open("myfile.dat",ios::out); call this function to read the file after all of your names are entered: (Toggle Plain Text) void ReadFile (void) { ifile.open("myfile.dat"); string x; while(ifile >> x) { cout << x; cout << endl; } ifile.close(); } void ReadFile (void) { ifile.open("myfile.dat"); string x; while(ifile >> x) { cout << x; cout << endl; } ifile.close(); } __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Sep 20th, 2005, 3:25 PM	#7
Infinite Recursion Programming Guru Join Date: Jul 2004 Location: United States Posts: 3,467 Rep Power: 8	Disregard my code above... Keep in mind that using OUT on your data file, will overwrite anything that's in it each time the file is opened for output. You will need to use APP to append data in cases like this. Here's how I would have went about it... you will need to turn it into OOP, etc. (Toggle Plain Text) #include <iostream> #include <fstream> #include <cstdlib> #include <string> using namespace std; void WriteToFile (string data); void ReadFile (void); ofstream ofile; ifstream ifile; int main (void) { char name[256]; while (strcmp(name,"n") != 0) { cout << "Enter name: "; cin.getline(name,200,'\n'); if (strlen(name) > 2) WriteToFile (name); } ReadFile(); system("PAUSE"); return 0; } void WriteToFile (string data) { ofile.open("myfile.dat",ios::app); //open a file ofile << data << endl; //write to it ofile.close(); //close it } void ReadFile (void) { char ch; ifile.open("myfile.dat"); while(!ifile.eof()) { char temp[256]; ifile.getline(temp,256); cout << temp << endl; } } #include <iostream> #include <fstream> #include <cstdlib> #include <string> using namespace std; void WriteToFile (string data); void ReadFile (void); ofstream ofile; ifstream ifile; int main (void) { char name[256]; while (strcmp(name,"n") != 0) { cout << "Enter name: "; cin.getline(name,200,'\n'); if (strlen(name) > 2) WriteToFile (name); } ReadFile(); system("PAUSE"); return 0; } void WriteToFile (string data) { ofile.open("myfile.dat",ios::app); //open a file ofile << data << endl; //write to it ofile.close(); //close it } void ReadFile (void) { char ch; ifile.open("myfile.dat"); while(!ifile.eof()) { char temp[256]; ifile.getline(temp,256); cout << temp << endl; } } __________________ http://jasonpowers.net "There are a thousand hacking at the branches of evil to one who is striking at the root."

Sep 20th, 2005, 2:01 PM	#2
Dan Newbie Join Date: Sep 2005 Posts: 7 Rep Power: 0	I don't know what's up with the smiley faces in the code... sorry

Sep 20th, 2005, 3:26 PM	#8
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	If you use ios::app, be sure and use ios::binary, too, or it won't work as you expect. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Sep 20th, 2005, 7:46 PM	#9
Dan Newbie Join Date: Sep 2005 Posts: 7 Rep Power: 0	I'm stumped but first thanks to all of you for taking the time to reply. Infinite recursion, a special thanks for writing out the code for me...your's worked like a charm and I'm going to save it. Following DaWei and your example I tossed the ios::out and added ios::binary and ios::app. My program still doesn't print out all of the names, only the last one entered. Sorry for being so insistant with getting my version to work but it's the format we're commenting with in class so I'd like to get it to work and understand why. Would it be possible to modify it only slightly and have it to work? ..here's the new code with app and binary....same result as before. (Toggle Plain Text) #include <conio.h> #include <iostream.h> #include <fstream.h> #include <stdio.h> class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; cin>>name; } void My_class::printnames() { cout<<"\nName = "<<name; cout<<flush; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::binary\|ios::app); do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cout<<"\nWould you like to enter another name? y/n "; }while(getch()!='n'); namefile.close(); namefile.open("myfile.dat",ios::binary\|ios::in); namefile.seekg(0); while(namefile.read((char)&X,sizeof(My_class))); { X.printnames(); } namefile.close(); getch(); return 0; } #include <conio.h> #include <iostream.h> #include <fstream.h> #include <stdio.h> class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; cin>>name; } void My_class::printnames() { cout<<"\nName = "<<name; cout<<flush; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::binary\|ios::app); do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cout<<"\nWould you like to enter another name? y/n "; }while(getch()!='n'); namefile.close(); namefile.open("myfile.dat",ios::binary\|ios::in); namefile.seekg(0); while(namefile.read((char)&X,sizeof(My_class))); { X.printnames(); } namefile.close(); getch(); return 0; }

Sep 20th, 2005, 8:14 PM	#10
Scorpions4ever Programmer Join Date: Jun 2005 Posts: 86 Rep Power: 4	This is why you should always put some error checking in your code. If you'd checked namefile.good() after the first namefile.open(), you would have realized that the file wasn't opened for write properly at all. You really need to open it with: (Toggle Plain Text) namefile.open("myfile.dat",ios::binary\|ios::app\|ios::out); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } namefile.open("myfile.dat",ios::binary\|ios::app\|ios::out); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } Note the extra ios parameter I added. If you don't have it, your open() will fail. With that said, you haven't handled reading it back correctly either. Here's how to really do it: (Toggle Plain Text) #include <iostream> #include <fstream> #include <cstdio> using namespace std; class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; cin>>name; } void My_class::printnames() { cout<<"\nName = "<<name; cout<<flush; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::binary\|ios::app\|ios::out); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cin.ignore(1); cout<<"\nWould you like to enter another name? y/n "; }while(getchar()!='n'); namefile.close(); namefile.open("myfile.dat",ios::binary\|ios::in); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } namefile.seekg(0); while(!namefile.eof()) { namefile.read((char)&X,sizeof(My_class)); X.printnames(); } namefile.close(); getchar(); return 0; } #include <iostream> #include <fstream> #include <cstdio> using namespace std; class My_class { private: char name[20]; public: void enternames(); void printnames(); }; void My_class::enternames() { cout<<"\nEnter a name : "; cin>>name; } void My_class::printnames() { cout<<"\nName = "<<name; cout<<flush; } int main(void) { fstream namefile; My_class X; namefile.open("myfile.dat",ios::binary\|ios::app\|ios::out); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } do{ X.enternames(); namefile.write((char)&X,sizeof(My_class)); cin.ignore(1); cout<<"\nWould you like to enter another name? y/n "; }while(getchar()!='n'); namefile.close(); namefile.open("myfile.dat",ios::binary\|ios::in); if (!namefile.good()) { cerr << "Open failed" << endl; return -1; } namefile.seekg(0); while(!namefile.eof()) { namefile.read((char)&X,sizeof(My_class)); X.printnames(); } namefile.close(); getchar(); return 0; }

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Programming Forums > Application Development > C++

File stream problems