C - dynamic arrays of structures - c

Question

I have a problem with a rather big piece of code. Knowing myself, it's some kind of a silly mistake, or, more likely, lack of understanding of pointers. I really need some help, so if someone could look at it I would be so grateful! I'm going to explain it now.
It's a program for my programming class. The teacher gave us a number (N) and a letter (X) in a txt file, and wants us to create a structure with three fields(int, char and float), and then four functions:
function #1 takes the number N as an argument and dynamically allocates memory for an array of pointers to N structures. then it assigns values to the fields in the structures - int and char are set to random values, and the float field is set to the number of the structure. the function returns the address of the array.
function #2 takes the size of the created array (the number of pointers in it) and a pointer to the array as arguments and deletes the array, freeing the memory.
function #3 takes the size of the created array and a pointer to the array as arguments, and then sorts the structures based on the int field, using bubble sort
function #4 searches through the structures and counts how many times the letter (X) is repeated in the char fields of the structures.
Here's the code with comments and errors. Please, can someone explain what am I doing wrong? To be honest I'm almost out of time, but I'm willing to stay up all night to understand and fix this.
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <time.h>
struct Foo {
int fieldint;
char fieldchar;
float fieldfloat;
};
Foo *initialize(int N);
int sort(int N, Foo *tablica);
int count(int N, Foo *tablica, char*X);
int deleting(int N, Foo **tablica);
int main () {
//this reads the number N and the letter to find from the .txt file:
FILE *file = fopen("inlab01.txt", "r");
int number;
char letter[1];
if (file == NULL) {
printf("Error opening file");
exit(-1);
}
while (fscanf(file, "%d%s", &number, letter) != EOF);
fclose(file);
//creating the array
//again, it's supposed to be an array of pointers to N structures:
Foo *arr[number];
*arr = initialize(number);
//sorting:
sort(number, *arr); //the program crashes at this function
//counting how many times the given letter appears:
//count(number, *arr, letter);
//we're supposed to print the first 20 of the structures
//this loop prints one structure and then the program crashes
for(int i=0;i<20;i++) {
printf("Structure %d:\nfield int:%d\nfield char:%c\nfield float:\f\n\n", i+1, arr[i]->fieldint, arr[i]->fieldchar, arr[i]->fieldfloat);
}
//deleting:
deleting(number, arr);
getch();
return 0;
}
Foo *initialize(int N) {
Foo **array;
array = (Foo **)malloc(sizeof(Foo) * N);
srand( time( NULL ) );
for(int i=0; i<N; i++) {
array[i] = (Foo*)malloc(sizeof(Foo));
array[i] -> fieldint = rand(); //random number
array[i] -> fieldchar = ( char )( rand() % 24 ) + 65; //random letter
array[i] -> fieldfloat=i;
}
return *array;
}
int sort(int N, Foo *array) {
int temp;
for (int i=0;i<N;i++){
for (int j=N-1;j>=j;j--) {
if(array[j].fieldint < array[j-1].fieldint) {
temp = array[j-1].fieldint;
array[j-1].fieldint = array[j].fieldint;
array[j].fieldint = temp;
}
}
}
return 0;
}
int count(int N, Foo *array, char*X){
int counter = 0;
for(int i=0;i<N;i++) {
if (array[i].fieldchar == 'X') {
counter = counter+1;
}
}
return counter;
}
int deleting(int N, Foo **array) {
for (int i=0;i<N;i++) {
free(array[i]);
}
free(array);
return 0;
}
The whole thing compiles, but then the program crashes instead of doing anything, really.
Please help.

Answer 1

struct Foo
{
int fieldint;
char fieldchar;
float fieldfloat;
};
Foo **array;
array = (Foo **)malloc(sizeof(Foo) * N);
You are compiling this code in C++. You want to use a C compiler, and you have to change the code to the following:
struct Foo **array;
You would use struct Foo everywhere, and you don't need that cast. Or declare the structure with typedef
Secondly, Foo **array is for allocating a 2-dimensional array. The way you are allocating 2-D array is wrong. Besides, you only need a 1-dimensional array Foo arr[number]
for (int j=N-1;j>=j;j--)
Note you have an error in your sort function (j >= j) is always true. Fix the sort function, avoid allocating a 2-D array and you are done.
int sort(int N, struct Foo *array)
{
int temp, i, j;
for (i = 0; i< N; i++) {
for (j = i + 1; j < N; j++) {
if (array[i].fieldint > array[j].fieldint) {
temp = array[i].fieldint;
array[i].fieldint = array[j].fieldint;
array[j].fieldint = temp;
}
}
}
return 0;
}
int main()
{
srand((unsigned)time(NULL));
int number = 3;
struct Foo arr[number];
int i;
for (i = 0; i < number; i++) {
arr[i].fieldint = rand(); //random number
arr[i].fieldchar = 'A' + (char)(rand() % 26); //random letter
arr[i].fieldfloat = (float)i;
}
sort(number, arr);
for (i = 0; i < number; i++)
printf("Structure %d:\nfield int:%d\nfield char:%c\nfield float:%f\n\n",
i + 1, arr[i].fieldint, arr[i].fieldchar, arr[i].fieldfloat);
getch();
return 0;
}
Note that your sort function swaps fieldint but Foo has other members, you probably want to swap all members if your goal is to swap the object.