C programming, dynamic allocation + linked lists
I am having problems with this code and I am not sure what I am doing wrong
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
typedef struct flight_struct{
char flightNum[7];
char originAirport[5];
char destAirport [5];
int timestamp;
struct flight_struct *next;
} flightRec;
int main(){
struct flight_struct *head; // unchanging first node.
struct flight_struct *tail; //the conductor.
struct flight_struct *p; // first new struct
FILE* binFile = fopen("acars.bin","r");
FILE* DataOut;
p =(struct flight_struct*) malloc(sizeof(*p) + 1); //malloc the first struct\
fread(p,sizeof(*p),1,binFile); //read the file into it.
head = p; //make head point to that struct
tail = p; //make tail point to that struct
// fclose(binFile);
while (feof(binFile) == 0){
flight_struct *temp = (struct flight_struct*) malloc(1*sizeof(*temp) + 1); //malloc a new struct
fread(temp,sizeof(*temp),1,binFile); //read the next struct from acars.bin into the structure you malloc'ed
temp -> next = NULL; // add that struct to your linked list using the next memeber of the struct
tail -> next = temp; // set tail to point to the element you just added
tail = tail -> next;
} //while not eof on acars file
tail = head;
while(tail -> next != 0 ){
int t;
t = tail -> timestamp;
time_t tim = t;
printf("%s, %s, %s, %s\n\n",tail -> flightNum,tail -> originAirport,tail -> destAirport,asctime(gmtime(&tim)));
tail = tail -> next;
} //starting at head traverse the list printing the leemnts of each strucure
}
Now what I get as a result is 
What I have to get is 
To be honest, I don't know what I am doing wrong and the help would be nice. That being said, I cannot use arrays, so a linked list is the only way to do it.
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Here's a solution that works:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
typedef struct flight_struct{
char flightNum[7],originAirport[5], destAirport [5];
size_t timestamp;
struct flight_struct *next;
} flightRec;
int readFlight(FILE* file, flightRec *fr);
int main() {
FILE *f = fopen("input.txt", "r");
if (f != NULL) {
while (feof(f) == 0) {
flightRec fr;
if (readFlight(f, &fr) == 0) {
printf("%s, %s, %s, %s\n", fr.flightNum, fr.originAirport,
fr.destAirport, ctime((time_t*)(&fr.timestamp)));
}
else {
fprintf(stderr, "Couldn't read the file information");
break;
}
}
}
fclose(f);
return 0;
}
int readFlight(FILE* file, flightRec *fr) {
struct tm tstr;
char *buffer = NULL, time[40];
size_t len = 0;
getline(&buffer, &len, file);
int v = sscanf(buffer, "%6s%*[^ ]%4s%*[^ ]%4s%*[^a-zA-Z]%[^\n\r]", fr->flightNum, fr->originAirport,
fr->destAirport, time);
free(buffer);
if (v == 4) {
strptime(time, "%a %b %d %T %Y", &tstr);
tstr.tm_isdst = -1;
fr->timestamp = (size_t)mktime(&tstr);
return 0;
}
return -1;
}
Input file:
XE4608, KIAH, KRSW, Mon Oct 21 15:25:00 2013
XE4232, KSDH, KASW, Sat Mar 29 16:38:00 2014
XE3453, MASH, KRSW, Wed Jan 01 19:10:00 2014
ZF4608, SAAH, KRSW, Tue Mar 25 18:49:00 2014
Output:
XE4608, KIAH, KRSW, Mon Oct 21 15:25:00 2013
XE4232, KSDH, KASW, Sat Mar 29 16:38:00 2014
XE3453, MASH, KRSW, Wed Jan 1 19:10:00 2014
ZF4608, SAAH, KRSW, Tue Mar 25 18:49:00 2014
Made the structure change to timestamp
be size_t
, not int
.
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You shouldn't have pointers in your file.
Because the order of the items in the file automatically sets the order in your list (obviously). I doubt the file contains pointers to sctructure and everything is fine (pointers may differ across architectures, ta-da).
What to do?
Given data structure:
struct flight_struct {
char flightNum[7];
char originAirport[5];
char destAirport [5];
int timestamp;
}
Implement list structure:
struct list {
flight_struct* data;
list* next;
list* prev; //if you want bi-directional list
}
And load from file only data structure to list structure.
The pointers in the binary are incorrect and can cause a lot of problems. Did you create a file with objects yourself or from another source?
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