allocate memory and read input from file to arrays of structures - c

Question

I have question about reading data from file to structures
when I tried to run this code i get unhandled exception Access violation reading location 0xcccccce0, The error occur inside the getData function, Why am I getting this error, how Should I fix the code ?
this is my input file
4
A,10
B,12
C,60
D,120
tutorY
my intention in the getData function was to first read the first line to get then number 4, then use that number to allocate for student structure and then read the next four lines of the file in to student structure fields and then read the last line into tutorname feild in the TUTOR structure.
thank in advance
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "queue.h"
#include "stack.h"
#define RECORDS_SIZE 100
#define NAME_SIZE 20
typedef struct Student
{
char nameStudent[NAME_SIZE];
int TimeIn;
int TimeUpdate;
}STUDENT;
typedef struct TUTOR
{
char nameTutor[NAME_SIZE];
int TutorTIme;
STUDENT *ptr;
}TUTOR;
QUEUE *queue1;
STACK *stack1;
void getData(STUDENT *studentArr[RECORDS_SIZE], TUTOR tutorArr[1]);
int main (void)
{
STUDENT *studentArr[RECORDS_SIZE];
TUTOR tutorArr[1];
FILE *fp = NULL;
getData(studentArr, tutorArr);
return 0;
}
void getData(STUDENT *studentArr[RECORDS_SIZE], TUTOR tutorArr[1])
{
FILE *fp;
char fileName[NAME_SIZE];
char buffer[RECORDS_SIZE];
int first = 0;
int count = 1;
printf("Enter file name: ");
gets(fileName);
fp = fopen(fileName, "r");
if (fp == NULL)
{
printf("Error! The file does not exist!\n");
}
fscanf(fp,"%d",&first);
*studentArr = (STUDENT*) malloc(first*sizeof(STUDENT));
while( fgets(buffer, first +1, fp) != NULL)
{
if (count <= first)
{
sscanf(buffer, "%[,]%d", studentArr[count]->nameStudent, studentArr[count]->TimeIn);
printf("%s,%d", studentArr[count]->nameStudent, studentArr[count]->TimeIn);
}
else
sscanf(buffer, "%s", tutorArr[count].nameTutor);
count++;
}
return;
}

Answer 1

There's a couple of problems I have spotted.
The first fscanf reading first will read the first number then leave the rest of the line ("\n") to be picked up by the first call to fgets
More importantly, studentArr is an array of pointers, presumably one element for each student, but the malloc allocates only the first pointer in sudentArr, all the others contain garbage, which is causing the access violation.

Answer 2

fix like this
void getData(STUDENT **studentArr, TUTOR tutorArr[1]);//change
int main (void)
{
STUDENT *studentArr;//change
TUTOR tutorArr[1];
FILE *fp = NULL;//not use
getData(&studentArr, tutorArr);//change
return 0;
}
void getData(STUDENT **studentArr, TUTOR tutorArr[1])
{
FILE *fp;
char fileName[NAME_SIZE];
char buffer[RECORDS_SIZE];
int first = 0;
int count = 1;
printf("Enter file name: ");
gets(fileName);//has risk
fp = fopen(fileName, "r");
if (fp == NULL)
{
printf("Error! The file does not exist!\n");
return;//add, can't continue
}
fscanf(fp,"%d\n",&first);//add, consumption '\n'
*studentArr = (STUDENT*) malloc(first*sizeof(STUDENT));
while( fgets(buffer, RECORDS_SIZE, fp) != NULL)//change buffer size
{
if (count <=first)//
{
sscanf(buffer, "%[^,],%d", (*studentArr)[count-1].nameStudent, &(*studentArr)[count-1].TimeIn);//add, `,` and -1 to count is 1 origin, `&` need for "%d"
printf("%s,%d\n", (*studentArr)[count-1].nameStudent, (*studentArr)[count-1].TimeIn);
++count;//need count up
}
else
sscanf(buffer, "%s", tutorArr[0].nameTutor);
}
return;//need allocate record size return to main
}

Answer 3

Some more problems:
count should be initialised to 0 not 1 because your array is zero-indexed.
You're not incrementing count in your loop
Allocate memory for each student inside the loop with studentArr[count] = new Student();
Prefer strtok to sscanf` to split the buffer into fields. Much easier to deal with the comma following the string.