Read a file through a function + Structure - c

Question

I have a structure, a txt file that I want to read and the following code that works fine.
I am trying to make a function to include most of the read file functions there but seem to have problems with local variables etc..
#include <stdio.h>
#include <string.h>
int i,j,numberofseats,temp;
char platenr[8],selection,buff[60];
char firstname[20];
char lastname[20];
char phone[11];
char *p;
typedef struct
{
char fullname[40];
unsigned short phonenr[10];
unsigned int seatnr;
}PASSENGERS;
int main(void)
{
FILE *businfo;
businfo = fopen ("bus.txt","r");
if (businfo == NULL)
{
printf("Error Opening File, check if file bus.txt is present");
exit(1);
}
fscanf(businfo,"%s %d",platenr, &numberofseats);
printf("Bus Licence plate Nr is: %s and number of seats is: %d", platenr, numberofseats);
PASSENGERS passenger[numberofseats];
for (j=0;j<numberofseats;j++)
{passenger[j].seatnr=j+1;
strcpy(passenger[j].fullname,"\0");
}
while (fgets(buff,sizeof(buff),businfo))
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(passenger[temp-1].fullname,firstname);
strcat (passenger[temp-1].fullname, " ");
strcat(passenger[temp-1].fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
(passenger[temp-1].phonenr[i])=*p -'0';
i++;
}
}
So after the code that works, this is the function I created,
where target should be defined, to update the structure
but the *target is not known yet since it is inside the txt file (the temp variable) that is going to be read by the function..
This is driving me nuts!
void readfile( PASSENGERS *target, FILE *businfo){
while (fgets(buff,sizeof(buff),businfo))
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(target->fullname,firstname);
strcat (target->fullname, " ");
strcat(target->fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
(target->phonenr[i])=*p -'0';
i++;
}
}}

Answer 1

Look at the difference between the readfile function you created and the pure code in main function. The problem is you fill correctly the array passengers by indexing each element (passenger[temp-1]) in your main function but the readfile function fills only the first element of the array each time the while loop is executed.
There are two solutions:
1st solution: the pointer target points to the same element (first one) once the function is executed (fill each element using (target+temp-1)-> )
void readfile( PASSENGERS *target, FILE *businfo)
{
while (fgets(buff,sizeof(buff),businfo))
{
sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy((target+temp-1)->fullname,firstname);
strcat ((target+temp-1)->fullname, " ");
strcat((target+temp-1)->fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
((target+temp-1)->phonenr[i])=*p -'0';
i++;
}
}
}
2nd solution: the pointer target points to the last non-null element in the array once the function is executed (increment the pointer at the end of while loop)
void readfile( PASSENGERS *target, FILE *businfo)
{
while (fgets(buff,sizeof(buff),businfo))
{
sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(target->fullname,firstname);
strcat (target->fullname, " ");
strcat(target->fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
(target->phonenr[i])=*p -'0';
i++;
}
target = target + temp - 1;
}
}

Answer 2

thanks for the advice everyone! I have the variables set as global because I will need them further down my program..
What I have done is transfer most of the file read code to the function that I set to have no iputs and outputs..
I also do the initialization of the structure by placing \0 into passenger names, and a seat nr from 1 to numberofseats..
I want for each line of the txt file the program to read the temp, and then in the structure PASSENGERS change the values passenger[temp]
The problem is that at this time everything gets ruined and when run it chaos appears with strange values.. I have included the whole code in case you want to run it, but the problem is only in the beginning..
#include <stdio.h>
#include <string.h>
int i,j,numberofseats,temp;
char platenr[8],selection,buff[60];
char firstname[20];
char lastname[20];
char phone[11];
char *p;
typedef struct
{
char fullname[40];
unsigned short phonenr[10];
unsigned int seatnr;
}PASSENGERS;
void readfile( void)
{
FILE *businfo;
businfo = fopen ("bus.txt","r");
if (businfo == NULL)
{
printf("Error Opening File, check if file bus.txt is present");
exit(1);}
else
{
fscanf(businfo,"%s %d",platenr, &numberofseats);
printf("Bus Licence plate Nr is: %s and number of seats is: %d", platenr, numberofseats);
PASSENGERS passenger[numberofseats];
for (j=0;j<numberofseats;j++)
{passenger[j].seatnr=j+1;
strcpy(passenger[j].fullname,"\0");
}
while (fgets(buff,sizeof(buff),businfo))
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
strcpy(passenger[temp-1].fullname,firstname);
strcat (passenger[temp-1].fullname, " ");
strcat(passenger[temp-1].fullname,lastname);
i=0;
for (p=phone;*p!='\0';p++)
{
(passenger[temp-1].phonenr[i])=*p -'0';
i++;
}
}
}
}
int main(void)
{
readfile();
PASSENGERS passenger[numberofseats];
do{
printf("\n\nNeo Sistima katagrafis thesewn leoforeiou\n");
printf("Please make a selection:\n\n");
printf("0. Exit\n");
printf("1. Empty Seats \n");
printf("2. Book Specific Seat \n");
printf("3. Advanced Search of booked Seats\n");
printf("4. Cancel Seat Booking\n");
printf("5. Show List of booked Seats\n");
scanf(" %c",&selection);
if (selection=='1')
{int freeseats = 0;
for (j=0; j<numberofseats; j++)
{
strcmp(passenger[j].fullname,"\0")==0 ? freeseats = freeseats + 1 : freeseats ;}
printf ("There are %d free seats in this bus \n", freeseats);
printf("Seats that are available are:\n");
for (j=0; j<numberofseats; j++)
{if (strcmp(passenger[j].fullname,"\0")==0)
printf ("%u\n", passenger[j].seatnr);
}
freeseats = 0;
}
else if (selection=='2')
{
printf("Please give seat nr (between 1 and %d) that you want to book:\n", numberofseats);
scanf("%d",&temp);
if (temp >numberofseats || temp <= 0)
{printf("Error: Seat nr should be between 1 and %d", numberofseats);}
else if (strcmp(passenger[temp-1].fullname,"\0")!=0)
printf("Error: Seat is already booked");
else
changeData(&passenger[temp-1]);
}
else if (selection=='3')
{
char tempsel,tmpfirst[20],tmplast[20];
unsigned short tempphone[10];
int counter, checkphone;
unsigned int tempseat;
printf("Do you want to search with Name (1) or Phone Nr (2)?\n");
scanf(" %c",&tempsel);
if (tempsel == '1')
{ printf("Enter passenger first name:");
scanf("%s",tmpfirst);
printf("Enter passenger last name:");
scanf("%s",tmplast);
strcat (tmpfirst, " ");
strcat(tmpfirst,tmplast);
for (j=0;j<numberofseats;j++)
if (strcmp(passenger[j].fullname,tmpfirst)==0)
printf ("passenger %s has seat nr #: %u\n",tmpfirst,passenger[j].seatnr);
}
else if (tempsel == '2')
{ checkphone=0;
printf("Enter passenger phonenr:");
for (i=0;i<10;i++)
scanf("%hu",&tempphone[i]);
for (j=0;j<numberofseats;j++)
{
counter=0;
for(i=0;i<10;i++)
{
if (passenger[j].phonenr[i]==tempphone[i])
counter=counter+1;
if (counter ==10)
{checkphone=1;
tempseat=passenger[j].seatnr;
}}
}
if (checkphone==1)
{printf ("passenger has seat #: %u\n",tempseat);
checkphone=0;}
}
}
else if (selection=='4')
{
printf("Please give seat nr (between 1 and %d) that you want to cancel booking:\n", numberofseats);
scanf("%d",&temp);
if (temp >numberofseats || temp <= 0)
{printf("Error: Seat nr should be between 1 and %d", numberofseats);}
else if (strcmp(passenger[temp-1].fullname,"\0")==0)
printf("Error: Seat is already free");
else
cancelSeat(&passenger[temp-1]);
}
else if (selection=='5') /*Menu 6 - Emfanisi listas kratimenon thesewn taksinomimenon kata ayksonta arithmo*/
{
printf("The following seats are booked: \n Name, PhoneNr, SeatNr\n\n"); /*Emfanisi minimatos*/
for (i=0; i<numberofseats; i++)
if (strcmp(passenger[i].fullname,"\0")!=0)
{
printf("%s, ",passenger[i].fullname);
for (j=0;j<10;j++)
{printf("%hu",passenger[i].phonenr[j]);}
printf(", %u\n",passenger[i].seatnr);
}
}
} while (selection!='0');
}

Answer 3

(You should have added the second version of your program to the question rather than posting it as an answer.)
What I have done is transfer most of the file read code to the function that I set to have no iputs and outputs..
The problem is that at this time everything gets ruined and when run it chaos appears with strange values..
That is because in the function readfile() the data is read into a local array passenger, which is deallocated upon block exit, and thereafter the program uses a homonymous, yet other array, which is uninitialized. To rectify that, allocate the array in readfile() so that (the address of) it can be returned from the function, and use the returned memory. Required changes:
void readfile( void)
{
…
PASSENGERS passenger[numberofseats];
…
{sscanf(buff, "%s %s %d %s", firstname, lastname, &temp,phone);
…
}
}
}
…
readfile();
PASSENGERS passenger[numberofseats];
to
PASSENGERS *readfile(void)
{
PASSENGERS *passenger;
…
passenger = malloc(numberofseats * sizeof *passenger);
if (!passenger) exit(!!numberofseats); // 0: no seats, 1: no memory
…
{ if (sscanf(buff, "%s %s %d %s",
firstname, lastname, &temp, phone) < 4) continue;
…
}
}
return passenger;
}
…
PASSENGERS *passenger = readfile();
Note that we have to check the return value of sscanf() - this is vital, since after the fscanf(businfo,"%s %d",platenr, &numberofseats), the first \n remains in the input stream buffer, so the first fgets reads an empty line.
Note also that you still have to work on the phone number storage, as Weather Vane wrote.