dealing with files and structures in c - c

Question

while i'm working on my manii project phonebook , i faced some problems in delete function when there are multi result for the same first name (i use first name to search about the contact that i want to delete)
in this case i made extra variable in my structure called "ID" and this ID Auto fill in my program (so each user has a unique id) , so i can later find exactly the result that the user want to delete it ,and it works fine , but when i delete a contact from the file it left me with a gap and this effect on the next contact
For Example :
i have 3 contacts each one has an iD 1 , 2 and 3 , when i delete No.2 , it become 1 and 3 , when i add a new user my Auto fill loop will count the number of the contacts (2) and give the new one ID of 3 , that left me with 3 contacts with ID of 1 , 3 , and 3 and this's wrong
so i came with an idea to Reset all the IDs after each Delete operation , it seems good for me and this few line should do it , i don't know why this part doesn't work , even i tried to put this loop in add() function so it should be good at this position too , but it doesn't work too
// reset all ids
rewind(ft);
int id=1;
while(fread(&p,sizeof(p),1,ft)==1)
{
p.id = id;
fwrite(&p,sizeof(p),1,ft);
id++;
}
This is my Full code with 0 Errors and 0 warning , and it work fine except the part of reset ids
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <string.h>
#include <conio.h>
struct address // nested
{
char city[30],
street[30];
int flat;
};
struct phonebook // main
{
int id;
char firstName[20],
lastName[20];
struct address add;
long int phNumber;
char email[50];
};
// functions ...
void launcher();
void menu();
void add();
void load();
void query();
void Delete();
void modify();
void back();
void scan(char *name);
int main()
{
system("color 1e");
printf("Let's start!\n");
launcher();
return 0;
}
void launcher()
{
menu();
}
void back()
{
menu();
}
void menu()
{
system("cls");
printf("\t\t *********** PhoneBook! *************");
printf("\n\n\t\t\t\t <| Menu |>\t\t\n\n");
printf("\t\t1.Add \t2.Load \t3.Query \n\t\t4.Modify \t5.Delete\t6.Exit\n");
switch(getch())
{
case '1' :
add();
break;
case '2' :
load();
break;
case '3' :
query();
break;
case '4' :
modify();
break;
case '5' :
Delete();
break;
case '6' :
printf("the program exit successfully");
exit(0);
break;
default:
system("cls");
int i;
for(i=15 ; i>-1 ; i--)
{
system("cls");
printf("\nInvalid key Entered , please enter any key from 1 to 6 only!\n");
printf("you will back to the main menu automatically in %d seconds",i);
Sleep(1000);
}
menu();
}
}
void add()
{
system("cls");
struct phonebook p; // local define
FILE *f;
f= fopen("data","ab+");
int id=1;
while(fread(&p,sizeof(p),1,f)==1)
{
id++;
}
printf("\nFirst Name : ");
scan(p.firstName);
printf("\nLast Name : ");
scan(p.lastName);
printf("\nEnter the address .. ");
printf("\n\tCity : ");
scan(p.add.city);
printf("\n\tStreet : ");
scan(p.add.street);
printf("\n\tFlat : ");
scanf(" %d",&p.add.flat);
printf("\nPhone number : ");
scanf(" %ld",&p.phNumber);
printf("\nEmail : ");
scan(p.email);
p.id=id; // Auto fill
fwrite(&p,sizeof(p),1,f); // saving the data into a file
fclose(f);
puts("\n\n\t\tdata is saved successfully!");
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
void load()
{
struct phonebook p;
system("cls");
FILE* f;
f = fopen("data","rb");
if(f==NULL)
{
puts("\n An error occur while opening the file >");
exit(1);
}
while(fread(&p,sizeof(p),1,f)==1)
{
printf("\n\n\t\t\t\t <| loading List |>\t\t\n\n");
printf("First name : %s\nLast name : %s\nAddress Info ...\nCity : %s\nStreet : %s\nFlat : %d\nPhone Number : %ld\nEmail : %s\nid : %d\n",p.firstName,p.lastName,p.add.city,p.add.street,p.add.flat,p.phNumber,p.email,p.id);
puts("\t\t * Enter any key to show more *");
getch();
system("cls");
}
fclose(f);
puts("\t\tno more data to show !");
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
void query()
{
system("cls");
struct phonebook p;
FILE* f;
f = fopen("data","rb");
if(f==NULL)
{
puts("\n An error occur while opening the file >");
exit(1);
}
char name[50];
int flag=0;
printf("please enter a name : ");
scan(name);
system("cls");
while(fread(&p,sizeof(p),1,f)==1)
{
if(strcmp(name,p.firstName)==0)
{
flag++;
printf("\n[%d] result found\n",flag); // ==> static text
printf("First name : %s\nLast name : %s\nAddress Info ...\nCity : %s\nStreet : %s\nFlat : %d\nPhone Number : %ld\nEmail : %s\n",p.firstName,p.lastName,p.add.city,p.add.street,p.add.flat,p.phNumber,p.email);
puts("");
}
}
if(flag == 0)
{
puts("file not found");
}
fclose(f);
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
void modify()
{
system("cls");
struct phonebook p,s;
FILE* f;
f = fopen("data","rb+");
if(f==NULL)
{
puts("\n An error occur while opening the file >");
exit(1);
}
char name[50];
int flag=0;
printf("please enter a name : ");
scan(name);
system("cls");
int results[50];
while(fread(&p,sizeof(p),1,f)==1)
{
if(strcmp(name,p.firstName)==0)
{
results[flag] = p.id;
flag++;
printf("\n\n >> full information about the result No. [%d] :- \n",p.id);
printf("First name : %s\nLast name : %s\nAddress Info ...\nCity : %s\nStreet : %s\nFlat : %d\nPhone Number : %ld\nEmail : %s\n",p.firstName,p.lastName,p.add.city,p.add.street,p.add.flat,p.phNumber,p.email);
}
}
if(flag == 0)
{
puts("file not found");
}
else
{
int choice,i,found=0;
int lastResultID = p.id;
puts("Please enter the Number of the result to confirm your order");
scanf(" %d",&choice);
// confirmation
for(i=0 ; i<flag ;i++){
if(results[i] == choice){
found =1;
break;
}
}
if(found == 0){
puts("\n Ops! Result not found.\nmaybe you entered a wrong No. OR an Error occurs Try again.");
Sleep(5000);
back();
}else{
//printf("\n%d\n",lastResultID);
puts("\n >> Are you want to modify this result ? type (Y) for Yes or (N) for No !");
char c = getch();
if( c == 'Y' || c == 'y')
{
system("cls");
printf("\nFirst Name : ");
scan(s.firstName);
printf("\nLast Name : ");
scan(s.lastName);
printf("\nEnter the address .. ");
printf("\n\tCity : ");
scan(s.add.city);
printf("\n\tStreet : ");
scan(s.add.street);
printf("\n\tFlat : ");
scanf(" %d",&s.add.flat);
printf("\nPhone number : ");
scanf(" %ld",&s.phNumber);
printf("\nEmail : ");
scan(s.email);
fseek(f,-sizeof(p)*(lastResultID-choice+1),SEEK_CUR);
s.id=choice;
fwrite(&s,sizeof(p),1,f); // saving
puts("\n\t\tyour data is modified!");
fclose(f);
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
else
{
system("cls");
puts("nothing change ! , press any key to back to the main menu !");
getch();
back();
}
}
}
}
void Delete()
{
int found =0;
system("cls");
struct phonebook p,s;
FILE* f;
FILE* ft;
f = fopen("data","rb");
ft = fopen("temp","ab+");
if(f == NULL || ft == NULL)
{
puts("\n An error occur while opening the file >");
perror("fopen() failed");
exit(1);
}
char name[50];
int flag=0,i;
int results[50];
printf("please enter a name : ");
scan(name);
system("cls");
while(fread(&p,sizeof(p),1,f)==1)
{
if(strcmp(name,p.firstName)==0)
{
results[flag] = p.id;
flag++;
printf("\n\n >> full information about the result No. [%d] :- \n",p.id);
printf("First name : %s\nLast name : %s\nAddress Info ...\nCity : %s\nStreet : %s\nFlat : %d\nPhone Number : %ld\nEmail : %s\n",p.firstName,p.lastName,p.add.city,p.add.street,p.add.flat,p.phNumber,p.email);
}
}
if(flag == 0)
{
puts("file not found");
}
else{
puts(" ");
int choice,check=0;
puts("please enter the number of the result which you want to delete");
scanf(" %d",&choice);
// confirmation
for(i=0 ; i<flag ;i++){
if(results[i] == choice){
check =1;
break;
}
}
if(check == 0){
puts("\n Oops! Result not found.\nmaybe you entered a wrong No. OR an Error occurred Try again later.");
Sleep(3500);
back();
}else{
puts("\n >> Do you want to delete this result ? type (Y) for Yes or (N) for No !");
char c = getch();
rewind(f); // reset the pointer
if( c == 'Y' || c == 'y')
{
system("cls");
while(fread(&p,sizeof(p),1,f)==1)
{
if(choice != p.id)
fwrite(&p,sizeof(p),1,ft);
if(choice == p.id)
found++;
}
//perror("fread() failed");
if(found == 0)
{
puts("An error occurred , please try again");
remove("temp");
Sleep(3500);
back();
fclose(f); // ==?
fclose(ft); // ==?
}
else
{
// reset all ids
rewind(ft);
int id=1;
while(fread(&p,sizeof(p),1,ft)==1)
{
p.id = id;
fwrite(&p,sizeof(p),1,ft);
id++;
}
fclose(f); // ==?
fclose(ft); // ==?
remove("data");
int c = rename("temp","data");
puts("file is deleted successfully");
if(c != 0)
perror("rename() failed"); // handling for rename error
}
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
else
{
system("cls");
puts("nothing changed ! , press any key to back to the main menu !");
getch();
back();
}
}
}
/*else
{
puts("\n >> Are you want to delete this result ? type (Y) for Yes or (N) for No !");
char c = getch();
if( c == 'Y' || c == 'y')
{
rewind(f);
while(fread(&p,sizeof(p),1,f)==1)
{
if(strcmp(name,p.firstName)!=0)
fwrite(&p,sizeof(p),1,ft);
}
fclose(f);
fclose(ft);
remove("data");
int c = rename("temp","data");
puts("file is deleted successfully");
if(c != 0)
perror("rename() failed");
// reset all ids
int id=1;
while(fread(&p,sizeof(p),1,f)==1)
{
p.id = id;
fwrite(&p,sizeof(p),1,f);
id++;
}
puts("\t\tEnter any key to back to the main menu");
getch();
back();
}
else
{
system("cls");
puts("nothing change ! , press any key to back to the main menu !");
getch();
back();
}
}*/
}
void scan(char *name)
{
int i=0,j;
char c,ch;
do
{
c=getch();
if(c!=8&&c!=13)
{
*(name+i)=c;
putch(c);
i++;
}
if(c==8)
{
if(i>0)
{
i--;
}
// printf("h");
system("cls");
for(j=0; j<i; j++)
{
ch=*(name+j);
putch(ch);
}
}
}
while(c!=13);
*(name+i)='\0';
}
Thanks in advance

Answer 1

What about using the highest id+1 instead of counting them?
int id = 1;
while(fread(&p,sizeof(p),1,f)==1)
{
if (p.id >= id) id = p.id+1;
}

Answer 2

You cannot interleave fread and fwrite without an intervening fseek:
7.21.5.3/7 When a file is opened with update mode ('+' as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file.