All content of file get duplicated while modifying a specific entry - c

Question

This code read/write data to/from binary file. Here modify() will take input from user, search for it in the file. If found, will prompt user to give new entry and the older entry would be replaced.
The question is, in modify() after fwrite() if I break the while loop then everything would be fine but, if I don't then the entry would still be modified but along with that the content of the file would be duplicated, why so ?
As in the beginning there are no duplicate entries in the file. So what I expect is, that even if I don't use break the loop should go on and finally terminate when whole file has been read. Here, the if(strcmp(e.name,user)==0) would only be true for one entry therefore the control should enter only once in this if block. Then how the entries are getting duplicated ?
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void add(FILE *);
void list(FILE *);
void modify(FILE *);
struct emp
{
char name[20];
int id;
float sal;
}e;
void add(FILE *f)
{
char *p=NULL;
printf("\nEnter name id sal\n");
scanf(" %s %d %f", e.name,&e.id,&e.sal);
fseek(f,0,SEEK_END);
if((fwrite(&e,sizeof(struct emp),1,f))==1)
{
printf("\nAdded Successfully\n");
}
else
{
printf("\nError wrting to file in ADD func\n");
}
}
void list(FILE *f)
{
rewind(f);
while(fread(&e,sizeof(struct emp),1,f)>0)
{
printf("\nRead %s %d %f\n",e.name,e.id,e.sal);
}
}
void modify(FILE *f)
{
char user[20];
char *p=NULL;
printf("\nEnter name to modify\n");
scanf(" %s", user);
rewind(f);
while(fread(&e,sizeof(struct emp),1,f)==1)
{
//printf("\n --------------- %s %d %f\n",e.name,e.id,e.sal);
if(strcmp(e.name,user)==0)
{
//fseek(f,-sizeof(struct emp),SEEK_CUR);
printf("\nEnter new name id salary\n");
scanf(" %s %d %f", e.name,&e.id,&e.sal);
fseek(f,-sizeof(struct emp),SEEK_CUR);
if(fwrite(&e,sizeof(struct emp),1,f)==1)
{
printf("\nModified successfull!!\n");
//break;
}
else
{
printf("\nError while modifying\n");
}
}
else
{
printf("\n\nstring not matched\n\n");
}
}
}
int main()
{
char val='T';
FILE *fp=NULL;
if((fp=fopen("database.dat","rb+"))==NULL)
{
if((fp=fopen("database.dat","wb+"))==NULL)
{
printf("\nError opening file in wb+ mode\n");
exit(0);
}
}
do
{
printf("\nEnter a to add, l to list, d to delete, m to modify and e to exit\n");
scanf(" %c", &val);
switch(val)
{
case 'a':
add(fp);
break;
case 'l':
list(fp);
break;
case 'm':
modify(fp);
break;
case 'd':
// del(fp);
break;
case 'e':
fclose(fp);
exit(0);
break;
default:
printf("\nInvalid Input\n");
break;
}
}
while(1);
}

Answer 1

I think it's a problem between fread() and fwrite().
After you use fwrite() to modify the emp, you continue the while loop without using fseek().
In fact, before, you used fseek() to go back and it was OK.
Now you have to place another fseek() which doesn't move, like this:
fseek(f, 0, SEEK_CUR);
Now you can remove the break and your Modify() function would seems like this:
void modify(FILE *f)
{
char user[20];
printf("\nEnter name to modify\n");
scanf("%s",user);
fflush(stdin);
rewind(f);
while(fread(&e,sizeof(struct emp),1,f)==1)
{
if(strcmp(e.name,user)==0)
{
printf("\nEnter new name id salary\n");
scanf("%s %d %f",e.name,&e.id,&e.sal);
fflush(stdin);
fseek(f,-sizeof(struct emp),SEEK_CUR);
if(fwrite(&e,sizeof(struct emp),1,f)==1)
{
printf("\nModified successfull!!\n");
//break; //This can be removed
fseek(f, 0, SEEK_CUR); //Place this here
}
else
{
printf("\nError while modifying\n");
}
}
else
{
printf("\n\nstring not matched\n\n");
}
}
}