How to write arrays of integers to binary files? - c

Question

Hello I am trying to write a program that stores two separate integer arrays and one float array, my code below does this but without the array part, in other words I can write a single digit to a file and print it back out, but I cannot find out how to do the exact same thing but with an array (Dynamically Allocated). Here is the code below: it takes three values (part number, quantity and price) and repeats taking the values in until the user enters 0 for part number (pn).
Then writes that data into a file called "inventory.txt", then in the same program, open the file for reading and display those values back on the terminal.
So far, the program can only handle one number in the variables at a time(duh), I just can't figure out how to do the same thing but with an array that gets bigger with each added element.
#include <stdio.h>
#include <stdlib.h>
int main(){
printf("This program stores an invetory: ");
int i=0, holdr, k; //declarations of needed variables
int pn, q;
float p;
FILE *fp;
fp=fopen("inventory.txt","w+b"); //open file
while(holdr!=0){ //aka while pn!=0, for some reason needed a separate variable to run loop coorectly
printf("Please enter item data (part number, quantity, price): ");
scanf("%d,%d,%f",*pn,*q,*p);//scan numbers into respective variables, need to turn these into ARRAYS
//pn = malloc((i+1) * sizeof(int)); (setting aside this part of code as I can't get it to work properly at all (for the dynamic aspect of the program(array increases in size as user enters more digits)))
//q = malloc((i+1) * sizeof(int));
//p = malloc((i+1) * sizeof(int));
fwrite(&pn,sizeof(int),1,fp); //write to file
fwrite(&q,sizeof(int),1,fp);
fwrite(&p,sizeof(int),1,fp);
holdr=pn; //set pn=holdr for the running loop
}
rewind(fp);//back to beginning of file
fp=fopen("inventory.txt","r+b"); //open for reading
if (fp == NULL){ //check for file
printf("nah");
exit(EXIT_FAILURE);
}
fread(&pn,sizeof(int),k,fp); //read and then print the values in the file stored in the specified variables, nned to turn these variables into ARRAYS
printf("%d\t" , **pn);
fread(&q,sizeof(int),k,fp);
printf("%d\t", **q);
fread(&p,sizeof(int),k,fp);
printf("%f\n", **p);
fclose(fp);//close file
return 0;}
Here is the second try I made, a lot closer, but it won't compile as the cast of malloc inside the while loop is incorrect and I have no idea what is the correct way to allocate the space through every iteration.
#include <stdio.h>
#include <stdlib.h>
int main(){
printf("This program stores an invetory: ");
int i=0, holdr, k;
int pn[1], q[1];
float p[1];
FILE *fp;
fp=fopen("inventory.txt","w+b");
while(holdr!=0){
printf("Please enter item data (part number, quantity, price): ");
scanf("%d,%d,%f",&pn[i],&q[i],&p[i]);
pn=malloc((i+1) * sizeof(int));
q=malloc((i+1) * sizeof(int));
p=malloc((i+1) * sizeof(float));
fwrite(&pn[i],sizeof(int),k+1,fp);
fwrite(&q[i],sizeof(int),k+1,fp);
fwrite(&p[i],sizeof(float),k+1,fp);
holdr=pn[i];
i++;
}
rewind(fp);
fp=fopen("inventory.txt","r+b");
if (fp == NULL){
printf("nah");
exit(EXIT_FAILURE);
}
fread(&pn,sizeof(int),k,fp);
printf("%d\t" , pn[2]);
fread(&q,sizeof(int),k,fp);
printf("%d\t", q[2]);
fread(&p,sizeof(int),k,fp);
printf("%f\n", p[2]);
fclose(fp);
return 0;}