junk display while accessing a .txt files throug c standard i/o calls

Hello friends,


in my below program iam opening doing add,display operations on .txt file.

Add operation is done properly , and in file also the data is storing as expected .

But while displaying records some garbage comes , and it doesnot print in a record by record format.

Iam using strtok here.

For debug purpose i print the buffer before strtok and after strtok , it shows some malfunction there.

Friends please guide if iam missing any thing here.

thanks in advance.

Code:

---

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define SUCCESS 0
#define DATA_BASE_ERR 1
#define ID_NOT_FOUND_ERR 2

#define REC_SIZE 28

typedef struct
{
  int studentId;
  char name[20];
  int phoneNum;
}student_t;

void strip_newline(char *name);
void disp_help();
int addNewStudentRec(FILE *fp,student_t *pS);
int dispAllStudentRecs(FILE *fp);
#if 0
int deleteStudentRec(FILE fp,int studentId);
#endif


int main()
{
  int option = 0,fd = 0,id = 0;
  student_t nRec;
  FILE *fp;

  memset(&nRec,0,sizeof(nRec));

  fp = fopen("student.txt","r+");

  if (!fp)
    {
      printf("Creating the file \n");
      fp = fopen("student.txt","w+");
      if (!fp)
        {
          printf("Could not create file \n");
          exit(1);
        }
    }

  disp_help();

  while(1)
    {
      printf("\n Enter Option: ");
      __fpurge(stdin);
      scanf("%d",&option);
      switch(option)
        {
          case 1:
            dispAllStudentRecs(fp);
            break;
        case 2:
          printf("Enter id name and phone \n");
          scanf("%d",&nRec.studentId);
          __fpurge(stdin);
          fgets(nRec.name,20,stdin);
          strip_newline(nRec.name);
          scanf("%d",&nRec.phoneNum);
          if(addNewStudentRec(fp,&nRec) != SUCCESS)
            printf("Record add operation failed \n");
          break;
#if 0
        case 3:
          printf("Enter id of record to delete :");
          scanf("%d",&id);
          if(deleteStudentRec(fd,id)!= SUCCESS)
            printf("Record delete operation failed \n");
          break;
#endif
        case 4:
          printf("Good bye \n");
          return SUCCESS;
        default:
          printf("Invalid option.Use the following \n");
          disp_help();
          break;
        }//switch
    }//while
  return SUCCESS;
}


void strip_newline(char *name)
{
  int len;

  len = strlen(name);
  if (name[len-1] == '\n')
    name[len-1] = 0;
}


void disp_help()
{
  printf("Enter 1 to display all records \n");
  printf("Enter 2 to add a record \n");
  printf("Enter 3 to delete a record \n");
  printf("Enter 4 to exit \n");
}


void line2rec(char *lbuf,student_t *pr)
{
  char *str;
  int len;
  str = (char *)strtok(lbuf,",\n");
  sscanf(str,"%d",&pr->studentId);
  str = (char *)strtok(0,",\n");
  len = strlen(str);
  str[len] = '\0';
  strcpy(pr->name,str);
  printf("before strtok line 2 rec %s\n",pr->name);
  str = (char *)strtok(0,",\n");
  sscanf(str,"%d",&pr->phoneNum);
  printf("after strtok line 2 rec %s\n",pr->name);

}




int dispAllStudentRecs(FILE *fp)
{
  int len;
  student_t rec;
  char lbuf[100];

  memset(&rec,0,sizeof(rec));
  memset(&lbuf,0,sizeof(lbuf));

  fseek(fp,0,SEEK_SET);
  len = fread(&lbuf,1,REC_SIZE,fp);
  if (len != REC_SIZE)
    {
      printf("No record to print \n");
      return ;
    }//if


  while(len == REC_SIZE)
    {
      line2rec(lbuf,&rec);
      if (rec.studentId != -1)
        {
          printf("%d,%20s,%d\n",rec.studentId,rec.name,rec.phoneNum);
        }//if
      memset(&lbuf,0,sizeof(lbuf));
      memset(&rec,0,sizeof(rec));
      len = 0;
      len = fread(&lbuf,1,REC_SIZE,fp);
    }//while

  return SUCCESS;
}//dispAllStudentRecs

int addNewStudentRec(FILE *fp,student_t *rec)
{
  int len;
  student_t trec;
  char lbuf[100];

  fseek(fp,0,SEEK_SET);
  while(1)
    {
      len = fread(lbuf,1,REC_SIZE,fp);
      if (len != REC_SIZE)
        {
          break;
        }
      line2rec(lbuf,&trec);
      if(trec.studentId == -1)
        {
          fseek(fp,REC_SIZE * -1,SEEK_CUR);
          fprintf(fp,"%d,%20s,%d\n",rec->studentId,rec->name,rec->phoneNum);
          return SUCCESS;
        }
    }
  fprintf(fp,"%d,%20s,%d\n",rec->studentId,rec->name,rec->phoneNum);

  return SUCCESS;
}

---

file student.txt :

# cat student.txt
101, Rama,101
102, Ravi,102


output :
-----------

./ex9.o
Enter 1 to display all records
Enter 2 to add a record
Enter 3 to delete a record
Enter 4 to exit

Enter Option: 1
before strtok line 2 rec Rama
after strtok line 2 rec Ramae
101, Ramae,101
before strtok line 2 rec Ravi
after strtok line 2 rec Ravi

102, Ravi
,10

First things first: If you're using gcc, always build with at least the -Wall flag. With your code, that should tell you that you have lots of functions implicitly declared, which means you forgot some headers. __fpurge() is nonstandard, so I'm not sure what header you'd need for that; but memset(), exit(), strlen(), and strcpy() are all missing declarations. Once you include stdlib.h and string.h, those warnings will disappear. As a result, you can remove the casts from your strtok() calls which, I presume, were added to silence the compiler.

The source of your problem might lie in how you're using fread(). fread() will not add a null character to the end of what it reads unless one happened to be present in the file. That means that fread() will not create strings! You must do that yourself by adding the null character—you know where to add it, because fread() tells you how many bytes it read.
EDIT: I just noticed that while you're not terminating the fread() in addNewStudentRec(), you are in dispAllStudentRecs() which appears to be the source of your problem; so you can probably disregard the above as not pertaining to the issue at hand, although you'll still want to terminate in addNewStudentRec().

I would also recommend using (void) when declaring functions that take no arguments. () means that a function takes an unspecified number of arguments, so the compiler won't complain if you pass it some.

You're reading the file using fread(), but writing to the file using fprintf().
Be consistent!

fread / fwrite or fprintf / fscanf

If you do that, then you can get rid of that line2rec thing.

Salem,

Iam folliwng your guidelines and using only fsacnf and fprintf.

Here i could not able to add the newline character to the file "\n".

next record always go to the first line it self.

And i could not display any records , every time it prints as if "No records present"

While adding the record it updates the data to .txt file only when i come out of the program.

Here is the program.


# cat ex9.c

Code:

---

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio_ext.h>

#define SUCCESS 0
#define DATA_BASE_ERR 1
#define ID_NOT_FOUND_ERR 2

#define REC_SIZE 30

typedef struct
{
  int studentId;
  char name[20];
  int phoneNum;
}student_t;

void strip_newline(char *name);
void disp_help(void);
int addNewStudentRec(FILE *fp,student_t *pS);
int dispAllStudentRecs(FILE *fp);

int main()
{
  int option = 0;
  student_t nRec;
  FILE *fp;

  memset(&nRec,0,sizeof(nRec));

  fp = fopen("student.txt","r+");

  if (!fp)
    {
      printf("Creating the file \n");
      fp = fopen("student.txt","w+");
      if (!fp)
        {
          printf("Could not create file \n");
          exit(1);
        }
    }

  disp_help();

  while(1)
    {
      printf("\n Enter Option: ");
      __fpurge(stdin);
      scanf("%d",&option);
      switch(option)
        {
          case 1:
            dispAllStudentRecs(fp);
            break;
        case 2:
          printf("Enter id name and phone \n");
          scanf("%d",&nRec.studentId);
          __fpurge(stdin);
          fgets(nRec.name,20,stdin);
          strip_newline(nRec.name);
          scanf("%d",&nRec.phoneNum);
          if(addNewStudentRec(fp,&nRec) != SUCCESS)
            printf("Record add operation failed \n");
          break;
        case 4:
          printf("Good bye \n");
          return SUCCESS;
        default:
          printf("Invalid option.Use the following \n");
          disp_help();
          break;
        }//switch
    }//while
  return SUCCESS;
}


void strip_newline(char *name)
{
  int len;

  len = strlen(name);
  if (name[len-1] == '\n')
    name[len-1] = 0;
}


void disp_help()
{
  printf("Enter 1 to display all records \n");
  printf("Enter 2 to add a record \n");
  printf("Enter 3 to delete a record \n");
  printf("Enter 4 to exit \n");
}

int dispAllStudentRecs(FILE *fp)
{
  int len;
  student_t rec;
  char lbuf[100];

  memset(&rec,0,sizeof(rec));
  memset(&lbuf,0,sizeof(lbuf));

  fseek(fp,0,SEEK_SET);
  len = fscanf(fp,"%d,%20s,%d",&rec.studentId,rec.name,&rec.phoneNum);

  if (len != REC_SIZE - 1)
    {
      printf("No record to print \n");
      return DATA_BASE_ERR;
    }//if

  while(len == REC_SIZE)
    {
    if (rec.studentId != -1)
        {
          printf("%d,%20s,%d\n",rec.studentId,rec.name,rec.phoneNum);
        }//if
      memset(&lbuf,0,sizeof(lbuf));
      memset(&rec,0,sizeof(rec));
      len = 0;
      len = fscanf(fp,"%d,%20s,%d",&rec.studentId,rec.name,&rec.phoneNum);
    }//while

  return SUCCESS;
}//dispAllStudentRecs

int addNewStudentRec(FILE *fp,student_t *rec)
{
  int len;
  student_t trec;
  char lbuf[100];
  char strRec[100];

  fseek(fp,0,SEEK_SET);
  memset(&lbuf,0,sizeof(lbuf));
  memset(&strRec,0,sizeof(strRec));

  while(1)
    {
    len = fscanf(fp,"%d,%20s,%d",&trec.studentId,trec.name,&trec.phoneNum);
      if (len != REC_SIZE)
          break;
      if(trec.studentId == -1)
          fseek(fp,REC_SIZE * -1,SEEK_CUR);
    }
    fprintf(fp,"%d,%20s,%d \n",rec->studentId,rec->name,rec->phoneNum);
  return SUCCESS;
}

---

cat student.txt
-------------------
101, Rehman,101102, Rashid,102

I think you have purge and scanf backwards here:

Code:

---

case 2:
          printf("Enter id name and phone \n");
          scanf("%d",&nRec.studentId);
          __fpurge(stdin);

---

Try flushing your fp output stream after each write.

(And, you never close your fp output file. Shame, shame.)

Quote:

---

Originally Posted by Dino

I think you have purge and scanf backwards here:

Code:

---

case 2:
          printf("Enter id name and phone \n");
          scanf("%d",&nRec.studentId);
          __fpurge(stdin);

---

Try flushing your fp output stream after each write.

(And, you never close your fp output file. Shame, shame.)

---

I'm pretty sure the __fpurge() is a "clean up anything left behind by scanf" rather than a flush operation.

--
Mats

Quote:

---

Originally Posted by matsp

I'm pretty sure the __fpurge() is a "clean up anything left behind by scanf" rather than a flush operation.

--
Mats

---

OK, I'll buy that. Then this code is backwards!!

Code:

---

while(1)
    {
      printf("\n Enter Option: ");
      __fpurge(stdin);
      scanf("%d",&option);

---

Quote:

---

Originally Posted by Dino

OK, I'll buy that. Then this code is backwards!!

Code:

---

while(1)
    {
      printf("\n Enter Option: ");
      __fpurge(stdin);
      scanf("%d",&option);

---

---

Maybe, but:

Code:

---

        fgets(nRec.name,20,stdin);

---

is the line immediately after the fpurge you posted about earlier. And fgets will "fail" if you leave the newline behind, like scanf does.

In the code reading the option, I presume it's just clearing out any rubbish left behind by any other input (e.g. someone entered "a" as the answer for option).

--
Mats

You also need to read the manual to find out what fscanf returns.
It isn't what you think.

salem & dino thanks for your suggestions,

now iam taking care of fscanf returntype , using fflush onthe file stream to stroe the records and closeing the file stream while exiting from the program.

Here i face a one problem with fscanf like below.

My record format is "101, Jhon,101"
Now when i do the fscnaf . like

fscanf(fp,"%d,%s,%d",&rec.studentId,rec.name,&rec. phoneNum);

Here it returns the number of items it read as only 2 , i.e rec.studenId = 101
and rec.name = "Jhone,101".
So no phoneNum, i feel even phone number is considered as string and its taking into rec.name argument.

Do i need to change the record format like "studentId,phoneNum,name" or else do i have any option of getting the arguments correctly .

thanks guys

Quote:

---

Originally Posted by vlrk

salem & dino thanks for your suggestions,

now iam taking care of fscanf returntype , using fflush onthe file stream to stroe the records and closeing the file stream while exiting from the program.

Here i face a one problem with fscanf like below.

My record format is "101, Jhon,101"
Now when i do the fscnaf . like

fscanf(fp,"%d,%s,%d",&rec.studentId,rec.name,&rec. phoneNum);

Here it returns the number of items it read as only 2 , i.e rec.studenId = 101
and rec.name = "Jhone,101".
So no phoneNum, i feel even phone number is considered as string and its taking into rec.name argument.

Do i need to change the record format like "studentId,phoneNum,name" or else do i have any option of getting the arguments correctly .

thanks guys

---

If I'm reading your question correctly, the answer is "just because you put a comma in the format string doesn't mean that %s is going to stop at a comma -- it will stop at a space (or tab, or enter-key) because that's how %s works". If you want to really stop at a comma, you can either (1) get the whole line with fgets and parse it yourself or (2) use a scanset (like %[^,]) to read up to a comma.

scanset worked for me now my fscanf looks like below

Code:

---

fscanf(fp,"%d,%[^,],%d",&trec.studentId,trec.name,&trec.phoneNum);

---

thans tabstop