storing dynamic arrays of a struct in text file in c language

Question

hello this is my first year in learning c programming , i spent all day trying to figure this one out and now i have a head ache anyway i just wanna keep this as simple as possible, here is a test code that i want to correct so i can understand how this works what i wanna do is store a dynamic array of structure variables in a text file, and then reading the data from that text file into a dynamic array. this is in c language

#include <stdio.h>
#include <stdlib.h>
struct student {
char nam[3];      // we store to this 
char testname[3]; // we read to this
}*science[10];
int main() {
int i;
FILE *ptr=fopen("science_class","a");
for (i=0;i<3;i++){          //storing the infro from dynamic array into the file
e[i]=(science*)calloc(3,sizeof(char));
puts("enter name");
gets(science[i]->name);
fprintf(ptr,"%s",science[i]->name);  }
for (i=0;i<3;i++){          // loading the info from the file to a dynamic array
fscanf(ptr,"%s",&science[i]->testname)
printf("name :%s \n",science[i]->testname) }
fclose(ptr);

}

Zoltán · Accepted Answer · 2016-03-10 09:06:48Z

I wrote a simple c program that has a car struct. The program simply reads data about cars into a dynamic array and writes it back to another file. Hope you understand the concepts:

#include<stdio.h>
#include<stdlib.h>

struct car
{
    char name[20];
    char color[20];
    float mass;
    int price;
};
typedef struct car Cars;

int main()
{
    int i, n;
    Cars *cars;
    ///////// READ:
    FILE *in = fopen("cars_in.txt", "r");
    fscanf(in, "%i", &n); //read how many cars are in the file
    cars = (Cars*)malloc(n*sizeof(Cars)); //allocate memory

    for (i = 0; i < n; ++i) //read data
    {
        fscanf(in, "%s", cars[i].name);
        fscanf(in, "%s", cars[i].color);
        fscanf(in, "%f", &cars[i].mass);
        fscanf(in, "%i", &cars[i].price);
    }

    fclose(in);


    ///////////// WRITE:
    FILE *out = fopen("cars_out.txt", "w");
    fprintf(out, "%d\n", n); 
    for (i = 0; i < n; ++i) 
    {
        fprintf(out, "%s ", cars[i].name);
        fprintf(out, "%s ", cars[i].color);
        fprintf(out, "%f ", cars[i].mass);
        fprintf(out, "%i\n", cars[i].price);
    }

    fclose(out);
    free(cars);
    return 0;
}

and here is some data that you should put in a cars_in.txt:

5
BMW red 1500 80000
Opel black 950 15000
Mercedes white 2500 100000
Ferrari red 1700 2000000
Dodge blue 1800 750000

EDIT: I simply changed fscanf to scanf and works fine. Be careful when you enter the data: first you have to tell how many cars you want to add so malloc can reserve space, after you enter the car's name->color->mass->price separated with white characters (enter, space, tab). Just change the read section, the rest of the code remains the same:

///////// READ FROM KEYBOARD

scanf("%d", &n); // first we have to know the number of cars

cars = (Cars*)malloc(n*sizeof(Cars)); //allocate memory

for (i = 0; i < n; ++i) //read data -> be careful: you have to keep the order
{
    scanf("%s", cars[i].name);
    scanf("%s", cars[i].color);
    scanf("%f", &cars[i].mass);
    scanf("%i", &cars[i].price);
}

what this one does is that it takes the content of the first file, and it copies it on to the second file, i replaced the first fscanf lines with this scanf("%s", cars[i].name); scanf("%s", cars[i].color); scanf("%f", &cars[i].mass); scanf("%i", &cars[i].price); so i can manualy input data but the program cruchs after i was done typing them in which means i still cant store data in a text file coould u please help me with that
sorry i replied so late, and hope you understand, i don't speak English very well
sorry i just got the chance to reply , thank you so much for the help, it helped me make sense of how this works, im very greatful for ur help

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