How can I read data from file? - c

Question

I'm trying to create phone book which has five function in c. I have formed just first function which takes and saves in file people's knowledge. However, I cannot succeed the second function which search just a person's (Not all people) knowledge from file.
To run this function (""display() function"") I want to a name from user to search and to display that name's knowledge on the screen. I wrote something but it didn't work. The problem is display() function. How can I read just one line and print it on the screen? Thanks in advance.
#include <stdio.h>
#include <stdlib.h> // "stdlib" library contains of exit() and malloc function
#include <Windows.h> // "Windows" library contains of Sleep() function
#include <string.h> // "string" library contains of strcmp() function
struct personKnowledge
{
char number[16];
char name[16];
char surname[16];
};
void newRecord();
void display();
void deletE();
void add();
void update();
FILE *ptrFILE;
int main()
{
int choice;
printf("\n\t\t *-* Phone Book Program *-*");
do
{
printf("\n\n\t\t 1) New record"); // The options are being presented to user
printf("\n\n\t\t 2) Display person knowledge");
printf("\n\n\t\t 3) Delete someone");
printf("\n\n\t\t 4) Add new person");
printf("\n\n\t\t 5) Update person knowledge");
printf("\n\n\t\t 6) Exit");
printf("\n\n\nEnter your choice: ");
scanf("%d", &choice);
switch (choice)
{
case 1:
{
newRecord();
break;
}
case 2:
{
display();
break;
}
case 3:
{
break;
}
case 4:
{
break;
}
case 5:
{
break;
}
case 6:
{
printf("\nWorking has been completed.\n");
exit(0);
break;
}
default:
{
printf("\nWrong entry! The program has been terminated.\n");
}
}
} while (choice >=1 && choice <=6 );
return 0;
}
void newRecord()
{
system("cls"); // Screen is being cleaned
if ((ptrFILE = fopen("Phone Book.txt", "w")) == NULL)
{
printf("The file couldn't open\n");
}
else
{
struct personKnowledge *p; // p means person
p = (struct personKnowledge *)malloc(sizeof(struct personKnowledge)); // Memory is being allocated
fflush(stdin);
printf("\n\nDetermine person name: "); // User is entering the person's knowledge and they are being saved in file
gets(p->name);
printf("Determine %s's surname: ", p->name);
gets(p->surname);
printf("Determine %s's number: ", p->name);
gets(p->number);
fprintf(ptrFILE, "Name\t\t\t\tSurname\t\t\t\t\tNumber\n");
fprintf(ptrFILE, "--------\t\t ----------------\t\t\t---------------------\n");
fprintf(ptrFILE, "\n%s%33s%38s\n", p->name, p->surname, p->number);
fclose(ptrFILE);
free(p);
printf("Please wait, information is saving to file..\n");
Sleep(1000);
printf("*-* Saving operation has been completed. *-*");
}
fclose(ptrFILE);
}
void display()
{
struct personKnowledge *s; // s means searching
char name[16];
if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
{
printf("The file couldn't open\n");
}
else
{
fseek(ptrFILE, 0L, SEEK_SET);
printf("Express name which you search: ");
gets(s->name);
while (!feof == NULL)
{
fscanf(ptrFILE,"%s", &name);
if (strcmp(s->name, name) == 0)
{
printf("qawsdsdf");
}
}
}
fclose(ptrFILE);
}

Answer 1

In answer to one of your questions, I recommend rewriting this loop in display()
while (!feof == NULL) // wrong way to use feof
{
fscanf(ptrFILE,"%s", &name); // might overflow the string space
if (s->name == name) // wrong way to compare strings
{
printf("qawsdsdf"); // missing newline?
}
}
with this
while (fgets(name, sizeof(name), ptrFILE) != NULL) // safer way to read to a small buffer
{
name [ strcspn(name, "\r\n") ] = 0; // remove trailing newline etc
if (strcmp(s->name, name) == 0) // compare the strings
{
printf("qawsdsdf\n"); // added newline
}
}
EDIT in any case your posted code does not even compile properly:
while (!feof == NULL)
is rubbish, it should have been
while (!feof(ptrFILE))
although as I said is not the way to use feof anyway. This would not have happened if you had compiler warnings enabled and dealt with them.

Answer 2

I think these minor changes will solve your problem
Allocate memory for storing personKnowledge s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge));
Make file pointer reach the starting location of data. A simple trick has been used to achieve this fscanf(ptrFILE, "Name\t\t\t\tSurname\t\t\t\t\tNumber\n");
fscanf(ptrFILE, "--------\t\t ----------------\t\t\t---------------------\n");
Make change in while loop.while (!feof(ptrFILE))
Scanning one row of data.fscanf(ptrFILE, "\n%s%33s%38s\n", s->name, s->surname, s->number)
Make change in string comparison.if (strcmp(name,s->name) == 0)
The modified display function
void display(){
struct personKnowledge *s;
s = (struct personKnowledge *)malloc(sizeof(struct personKnowledge)); // Memory is being allocated for s
fflush(stdin);
char name[16];
if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
{
printf("The file couldn't open\n");
}
else
{
fseek(ptrFILE, 0L, SEEK_SET);
printf("Express name which you search: ");
scanf("%s",name); //the name you want to retrieve
fscanf(ptrFILE, "Name\t\t\t\tSurname\t\t\t\t\tNumber\n");
fscanf(ptrFILE, "--------\t\t ----------------\t\t\t---------------------\n"); //when we read the file for first time we need to start from the first location of person data, this is a trick to make ptrFILE reach there
fflush(stdin);
while (!feof(ptrFILE))
{
fscanf(ptrFILE, "\n%s%33s%38s\n", s->name, s->surname, s->number);//same format as fprintf used in newRecord
if (strcmp(name,s->name) == 0) //comparison
{
printf("qawsdsdf");
}
}}fclose(ptrFILE);}

Answer 3

My solution was to change how the file is formatted
fprintf(ptrFILE, "\n%s%33s%38s", p->name, p->surname, p->number);
Because if you're using a program to retrieve information, there's no need to fill it with a bunch of junk headers every time you write to it.
I then edited the display function to be able to retrieve said information.
void display()
{
struct personKnowledge s; // s means searching
char name[16];
char sname[16];
char number[16];
char surname[16];
if ((ptrFILE = fopen("Phone Book.txt", "r")) == NULL)
{
printf("The file couldn't open\n");
}
else
{
printf("Express name which you search: ");
scanf("%s", &sname);
do
{
fscanf(ptrFILE,"%s%33s%38s", &name, &surname, &number);
if (strcmp(sname, name) == 0)
{
printf("%s %s %s", name, surname, number);
}
}
while (strcmp(sname, name) != 0);
}
}
P.S. I'm still new to c myself and I don't think I could give you a good explanation as to why my code works and yours doesn't. But I can say that those headers you were writing to the file every time was a major part of the problem when I was troubleshooting your code.