Saving Linked List

Hi everyone;
I made a linked list with a class called Patient, but in the loop where I go through each element, the programme doesnot work correctly(it Halts). It doesnt generate any compiler errors, it stops working whenever the function is provoked.
The following is the code of the function to save all entries in a file:

Code:

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void save(Patient* pNDS)
{
    FILE *fp;  // Declare a pointer to a file structurepNDS=pHead;
    fp = fopen("D:junk.txt", "w+");
    pNDS=pHead;
    while(pNDS)
    {//Cheap try to save in file
                  // This opens a file called
                      //junk.dat for writing (and reading)
                     
                      fprintf(fp, "%s\t",pNDS->m_Name);
                      fprintf(fp, "%d\t",pNDS->m_ID);
                      fprintf(fp, "%d\n",pNDS->m_DOB);
                      fprintf(fp, "%s\t",pNDS->m_Address);
                      fprintf(fp, "%s\t",pNDS->m_PreMed);
                     
                      pNDS=pNDS->pNext;
    }
    fclose(fp);

}

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If anyone can help or even comment, that would be great..............Thanks.

I am unaware of any file system where "D:junk.txt" is a valid filename. (EDIT: What am I thinking? It is valid on linux; don't know why I thought colon was a reserved character. However, I suspect you're not on a *nix system, so you will need a slash or two.) Even if you happen to be on such a file system, you should always check whether or not your fopen actually opened something. (EDIT: Also, post your C problems in the C forum.)

No I dont think that is the problem, I tried it just now and worked the same way. I used the same file writting code in the add(Patient* pNDS) function (that adds new objects to the list), it worked just fine, only problem is that it erases the previous entries and save only the last object.........so, any other ideas, maybe the sequence is wrong.?

You tried what just now and what worked the same way?

Code:

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void save(Patient* pNDS)

---

Code:

---

    pNDS=pHead;

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Why do you pass pNDS to save() then overwrite with the value of pHead?

Tim S.

Good point there stahta, so I tried this code and doesnt work either:

Code:

---

inline void save(Patient* pNDS)
{
    Patient* pL=pHead;
    FILE *fp;
    fp = fopen("D:\junk.txt", "w+");

    while(pL)
    {
                     
                      fprintf(fp, "%s\t",pNDS->m_Name);
                      fprintf(fp, "%d\t",pNDS->m_ID);
                      fprintf(fp, "%d\n",pNDS->m_DOB);
                      fprintf(fp, "%s\t",pNDS->m_Address);
                      fprintf(fp, "%s\t",pNDS->m_PreMed);
                     
                      pL=pL->pNext;
    }
    fclose(fp);

}

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Oh, By it I meant the backslash in the file name.

Here is the hole code:

Code:

---

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <string.h>
#include <fstream>
using namespace std;

class Patient
{
      public:
              static int count;
              int m_ID;
              int m_DOB;
              char m_PreMed[128];
              char m_Address[128];
              char m_Name[128];
              Patient* pNext;
};

Patient* pHead=0;
int Patient::count=0;

                     
// add function is outside the class(not member function)
void add(Patient* pNDS, int& refcount)
{
      //add new object
      pNDS->pNext=pHead;
      pHead=pNDS;
      //fill in its member data           
                  // Improvised part..WORKS!!
                  cout<<"Enter the Patients name (use underscores for spaces): ";
                      char namebuffer[128];
                      cin>>namebuffer;

                  strncpy(pNDS->m_Name,namebuffer,128);
                      pNDS->m_Name[127]='\0';
                     
                      cout<<"\nEnter the Patients ID: ";
                      int PatientID;
                      cin>>PatientID;
                      pNDS->m_ID=PatientID;
                     
                      cout<<"\nEnter the Patients year of birth: ";
                      int PatientDOB;
                      cin>>PatientDOB;
                      pNDS->m_DOB=PatientDOB;
                     
                      cout<<"\nEnter the Patients address: ";
                      char addressbuffer[128];
                      cin>>addressbuffer;
                      strncpy(pNDS->m_Address,addressbuffer,128);
                      pNDS->m_Address[127]='\0';
                     
                      cout<<"\nEnter Patients previous medications: ";
                      char premedbuffer[128];
                      cin>>premedbuffer;
                      strncpy(pNDS->m_PreMed,premedbuffer,128);
                      pNDS->m_PreMed[127]='\0'; 
                     
                      refcount++;
            }
           
           
           
           


// Save to file ()
inline void save(Patient* pNDS)
{
    Patient* pL=pHead;
    FILE *fp;
    fp = fopen("D:\junk.txt", "w+");

    while(pL)
    {
                     
                      fprintf(fp, "%s\t",pNDS->m_Name);
                      fprintf(fp, "%d\t",pNDS->m_ID);
                      fprintf(fp, "%d\n",pNDS->m_DOB);
                      fprintf(fp, "%s\t",pNDS->m_Address);
                      fprintf(fp, "%s\t",pNDS->m_PreMed);
                     
                      pL=pL->pNext;
    }
    fclose(fp);

}
           
           
int main()
{
    Patient objpat;
    Patient::count=0;
    //menu simulation
   
    char cChoice;
    do
    {
        cout<<"\tChoose the Operation by selecting the appropriate number:- "<<endl;
        cout<<"1) Create new Patient file.\n2) View All "<<Patient::count<<" entries.\n3) Quit."<<endl;
       
        int msg;
        cin>>msg;
    switch(msg)
    {
              case 1:
                    {
                        add(& objpat, Patient::count);
                        break;
                    }
              case 2:
                    {
                       
                            break;
                    }
              case 3:
                   
                    save(& objpat);
                    cChoice='Q';
                    break;
              default:
                      cout<<"Invalid number";
    }
    }while(cChoice!='Q');
   
    system("PAUSE");
    return 0;
}

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Please it has been bugging me for so long.............Thanks for your time.

"D:\\junk.txt"

backslash is an escape character.

A single backslash signifies escape to use a backslash in a literal you must use two backslashes:

Code:

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fp = fopen("D:\\junk.txt", "w+");

---

Quote:

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I am unaware of any file system where "D:junk.txt" is a valid filename. (EDIT: What am I thinking? It is valid on linux; don't know why I thought colon was a reserved character. However, I suspect you're not on a *nix system, so you will need a slash or two.)

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Actually that could be a valid file name in a Windows command shell as well.

Jim

Why are you mixing c and c++ file IO? Stick to C++ filesteams.

Thoughts:
- Dump char. Use std::string.
- Don't use cin >> with strings. Especially not C-style strings. That's just a disaster waiting to happen. Use std::getline for std::string.
- Don't mix C and C++ I/O. Stick with C++ I/O.
- Don't mix cin >> and std::getline. Or alternatively, use std::cin.ignore(...) after cin >>. This should become a problem after you switch.
- Don't use str(n)cpy. Use std::string and the normal assignment operator.
- Fix indentation.