Reading struct from binary file (C) - c

Question

I need your help with reading struct from binary file,
the "Grocery read_from_file ()..." function Can't get this to work!
Here is my code:
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <ctype.h>
#include <conio.h>
struct grocerylist
{
int iD;
char grocery[30];
float amount;
char unit[10];
};
Grocery set_size_of(Grocery* list, int index);
Grocery input(int index);
void print_grocerylist(Grocery* list, int* index);
void write_to_file(FILE* file_pointer, Grocery* list, int index);
Grocery read_from_file(FILE* file_pointer, Grocery* list, int* index);
void change_item(Grocery* list, int index);
void remove_item(Grocery* list, int* index);
int main()
{
Grocery* list = (Grocery*)malloc(sizeof(Grocery)*1); //Grocery-array allocated memory for 1 struct
int index = 0, choice = 0;
FILE* file_pointer = NULL;
printf("Hey there user!\n");
while(choice != 7){
system("cls");
printf("Menu\n");
printf("1 - Add an item to the list.\n2 - Print the contents of your current list.\n3 - Print the contents to file.\n4 - Read from file.\n5 - Change an item on the list.\n6 - Remove item from the list.\n7 - close the program.\nChoose: ");
scanf("%d", &choice);
printf("\n");
switch(choice){
case 1:
list[index] = input(index);
index++;
*list = set_size_of(list, index); //Reallocating memory for the array of grocery-structs.
fflush(stdin);
break; //Add item
case 2:
print_grocerylist(list, &index); //Print list
fflush(stdin);
break;
case 3:
write_to_file(file_pointer, list, index); //print to file
fflush(stdin);
break;
case 4:
*list = read_from_file(file_pointer, list, &index); //read from file
fflush(stdin);
break;
case 5:
change_item(list, index); //change item
fflush(stdin);
break;
case 6:
remove_item(list, &index); //remove item
index--;
fflush(stdin);
break;
case 7:
free(list);
exit(EXIT_SUCCESS); //End program
break;
default:
printf("Wrong input, please try again!");
fflush(stdin);
getch();
break;
}
}
return 0;
}
Grocery set_size_of(Grocery* list, int index){ //reallocates memory.
list = realloc(list, (index+1)*sizeof(Grocery));
return *list;
}
Grocery input(index){
Grocery tmp;
int x = 0;
tmp.iD = index +1;
fflush(stdin);
printf("Grocery: ");
gets(tmp.grocery);
while(x == 0){
fflush(stdin);
printf("Amount: ");
x = scanf("%f", &tmp.amount);
if(x == 0){
puts("Error, please try again!");
}
}
fflush(stdin);
x = 0;
while(x == 0){
printf("Unit: ");
gets(tmp.unit);
if(isalpha(*tmp.unit)){
x = 1;
}else{
x = 0;
puts("Error: please try again!\n");
}
}
printf("\n");
return tmp;
}
void print_grocerylist(Grocery* list, int* index){
int i;
system("cls");
printf("The grocery list contains:\n");
printf("Item Amount Unit");
for(i=0;i<*index;i++)
{
printf("\n%d: %-10s %5.1f %6s", list[i].iD, list[i].grocery, list[i].amount, list[i].unit);
}
printf("\n");
getch();
printf("Press any key to continue.\n");
}
void write_to_file(FILE* file_pointer, Grocery* list, int index){ //works just fine afaik.. Prints the index at the start, fills it up with all the rest.
char filename[30];
memset(filename, '\0', sizeof(filename));
printf("What is the name of the file you wish to write to?: ");
scanf("%s", filename);
strcat(filename, ".txt");
file_pointer = fopen(filename, "wb");
if(file_pointer == NULL){
printf("Error!");
return;
}else{
fflush(stdin);
printf("File opened successfully!\n");
fwrite(&index, sizeof(int), 1, file_pointer);
fwrite(list, sizeof(Grocery), index, file_pointer);
printf("File written.");
getch();
}
fclose(file_pointer);
return;
}
Grocery read_from_file(FILE* file_pointer, Grocery* list, int* index){ //Can't get this to work...
char filename[30];
memset(filename, '\0', sizeof(filename));
printf("What is the name of the file you wish to read from?: ");
scanf("%s", filename);
strcat(filename, ".txt");
file_pointer = fopen(filename, "rb");
if(file_pointer == NULL){
printf("Error!");
return *list;
}else{
fflush(stdin);
free(list);
printf("File opened successfully!\n");
fread(index, sizeof(int), 1, file_pointer);
printf("Index %d read.\n", *index);
list = (Grocery*)calloc(*index, sizeof(Grocery));
fread(list, sizeof(Grocery), (*index), file_pointer);
printf("File read.");
getch();
fflush(stdin);
}
fclose(file_pointer);
return *list;
}
void change_item(Grocery* list, int index){ //Basically it's a more complex version of "Grocery input()" were we look to the ID/index and alter the information.
int x = 0, id, item, choice;
print_grocerylist(list, &index);
printf("Which item would you like to change?\nID number: ");
scanf("%d", &id);
printf("\nWhat do you want to change?\n1 - Grocery.\n2 - Amount.\n3 - Unit.\nChoose: ");
scanf("%d", &choice);
switch(choice){
case 1:
fflush(stdin);
printf("Grocery: ");
for(item = 0; item <= index; item++){
if(list[item].iD == id){
gets(list[item].grocery);
}
}
break;
case 2:
while(x == 0){
fflush(stdin);
printf("Amount: ");
for(item = 0; item <= index; item++){
if(list[item].iD == id){
x = scanf("%f", &list[item].amount);
}
}
if(x == 0){
puts("Error, please try again!");
}
}
break;
case 3:
fflush(stdin);
x = 0;
printf("Unit: ");
for(item = 0; item <= index; item++){
if(list[item].iD == id){
gets(list[item].unit);
if(isalpha(*list[item-1].unit)){
x = 1;
}else{
x = 0;
puts("Error: please try again!\n");
}
}
}
break;
default:
printf("\nError! Please try again.\n");
break;
}
return;
}
void remove_item(Grocery* list, int* index){ //Takes the last struct and copies it to the slot which will be "removed" and then reallocates the memory for the array -1, keeping the old ID, to make things simple.
int item;
printf("Which item would you like to remove?\nID number: ");
scanf("%d", &item);
strcpy(list[item].grocery, list[*index].grocery);
list[item].amount = list[*index].amount;
strcpy(list[item].unit, list[*index].unit);
list = realloc(list, (*index-1)*sizeof(Grocery));
return ;
}

Answer 1

For the most part, the "Grocery read_from_file()" function works, but it returns only the first item instead of the list it correctly read.
To return and assign (a pointer to) the whole list, change the call
*list = read_from_file(file_pointer, list, &index);
to
list = read_from_file(file_pointer, list, &index);
and the definition
Grocery read_from_file(FILE* file_pointer, Grocery* list, int* index){
…
return *list;
…
return *list;
}
to
Grocery *read_from_file(FILE *file_pointer, Grocery *list, int *index)
{
…
return list;
…
return list;
}
To not leak the memory of the old list when it reads one from a file, insert free(list) before list = (Grocery*)calloc(*index, sizeof(Grocery)); or change that to
list = realloc(list, *index * sizeof(Grocery));