How do I make my code in C read and store a file

Question

I have been stuck on this for a while. I am not sure how to print our all the lines from my file in to C terminal and then save it into a data structure. My code is as following:

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

int main()
{
    printf("Hello world!\n");
    int i = 43;// number of iteration to save data in an array
    int x;
    FILE *fptr;
    struct values *valuesPtr, values[x];
    valuesPtr = &values[x];


        if((fptr = fopen("energy.txt", "r")) == NULL)
        {
            printf ("Error opening file ");
            return 0;
        }
        while (fptr != NULL)
        {
        for(x = 0; x < i; x++ )
        {
            fscanf(fptr, "%s %s %d", &valuesPtr->start_vertex, &valuesPtr->destination_vertex, &valuesPtr->num);
            printf("\nStart vertex: %s \nDestination vertex: %s \nWeight: %d\n\n", valuesPtr->start_vertex, valuesPtr->destination_vertex, valuesPtr->num);
        }
        }
       fclose(fptr);
    return 0;
}

My structure.h file has the following structure:

struct values{
        int num;
        char start_vertex[250];
        char destination_vertex[250];
        };

It currently only shows the first line from my file. I want it to read all the lines from the file and then save that data in a data structure. Could you also tell me what the best data structure I could use to save all of the elements from my file in memory to be used later on.

Answer 1

The way you initialize valuesPtr is not exact. valuesPtr = &values[x]; is failed because the maximum index that array values can take is x-1 (from 0 to x-1 ). It is a pointer, so allocate it (do not forget initialize x first):

 struct values *valuesPtr = malloc(sizeof(struct values) * x);
 if (!valuesPtr)
    return -1;

Or using 1D array:

/*init x here*/
struct values valuesPtr[x]

And if you want to get value by using fscanf , do not use & for char array. Use as below:

int num =  fscanf(fptr, "%s %s %d", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, &valuesPtr[i].num);
// verify the the number (num) of input items successfully matched and assigned if you want.

UPDATE test:

 struct values{
    int num;
    char start_vertex[250];
    char destination_vertex[250];
  };

int main()
{
    printf("Hello world!\n");
    int x = 3; // The number of lines that you want to get from file.
    FILE *fptr;
    struct values *valuesPtr = malloc(sizeof(struct values) * x);

    if (!valuesPtr)
        return -1;


    if((fptr = fopen("text.txt", "r")) == NULL)
    {
        printf ("Error opening file ");
        return 0;
    }

    for(int i = 0; i < x; i++ )
     {
            fscanf(fptr, "%s %s %d", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, &valuesPtr[i].num);
            printf("\nStart vertex: %s \nDestination vertex: %s \nWeight: %d\n\n", valuesPtr[i].start_vertex, valuesPtr[i].destination_vertex, valuesPtr[i].num);
     }
     free(valuesPtr);
     fclose(fptr);
    return 0;
}

text.txt

ab cd 9
ef gh 10
ii cc 11

The output:

Hello world!

Start vertex: ab 
Destination vertex: cd 
Weight: 9


Start vertex: ef 
Destination vertex: gh 
Weight: 10


Start vertex: ii 
Destination vertex: cc 
Weight: 11