Reading data from file into structure in c programming language

Question

I want to read data from txt file and save those data in variables not just print output. How do I save those data from text file in variables? I tried like this and it did not work out:

int value1 ; 
object2->value =&value1 ; 
*(object2->value) = value1 ; 

My txt file looks like this:

INT 
A
5

and my code looks like this:

#include <stdio.h>
#include <stdlib.h> // For exit()

struct variable {
    char type[10];
    char name[10];
    int value;
};

int main(){

struct variable *object2=malloc(sizeof(struct variable));

    FILE * file= fopen("input.txt", "rb");
    if (file != NULL) {
        fread(object2, sizeof(struct variable), 1, file);
        fclose(file);
    }
    
    int value1 ;
    object2->value =&value1 ;
    *(object2->value) = value1 ;

    printf("%d\n",value1);

    printf("%s/%s/%d\n",object2->type,object2->name,object2->value);
    
    
    }

Answer 1

File format:

CHAR
B
6
INT
A
5
FLOAT
C
7

This is my solution:

#include <stdio.h>
#include <stdlib.h> // For exit()
#include <string.h>

#define BUFF_SIZE 1024
#define NAME_TYPE_SIZE 10
#define VALUE_SIZE 20

#define NOT_ENOUGH_MEMORY 1
#define CANT_OPEN_FILE 2
#define FILE_ENDED 3
#define TOO_BIG_STR 4
#define CANT_FORMAT_VALUE 5
#define NOT_FOUND_LINE 6

#define SEARCH_NAME "A"

#pragma warning(disable : 4996) // for vs

struct variable {
    char type[NAME_TYPE_SIZE];
    char name[NAME_TYPE_SIZE];
    int value;
};

int find_var_in_file(char* file_path, char* find_name, struct variable* dest);

int main()
{
    struct variable* object2 = malloc(sizeof(struct variable));

    if (NULL == object2)
    {
        printf("not enough memory");
        return NOT_ENOUGH_MEMORY;
    }

    int error = find_var_in_file("input.txt", SEARCH_NAME, object2);

    if (CANT_OPEN_FILE == error)
    {
        return printf("can't open file");
    }

    if (error == 0)
    {
        // Printing data to check validity
        printf("read: type: %s name: %s value: %d", object2->type, object2->name, object2->value);
        int a = object2->value;
        // do stuff with a
    }
    else
    {
        if (error == NOT_FOUND_LINE)
        {
            printf("not find the var \"" SEARCH_NAME "\" in the file");
        }
        else
        {
            printf("error reading the file. error code: %d", error);
        }
    }

    free(object2);

    return 0;
}

int read_line(char* buffer, int buffer_size, char* dest, int dest_size, FILE* stream)
{
    if (!fgets(buffer, buffer_size, stream))
    {
        return NOT_FOUND_LINE;
    }

    int read_len = strlen(buffer);

    if ('\n' == buffer[read_len - 1])
    {
        if (read_len == 1)
        {
            return NOT_FOUND_LINE;
        }
        buffer[read_len - 1] = '\0'; // remove "\n" in the end
    }

    if (dest_size <= strlen(buffer)) // last chat is null
    {
        return TOO_BIG_STR;
    }

    strcpy(dest, buffer);

    // clear the read
    memset(buffer, '\0', read_len);

    return 0;
}

int find_var_in_file(char* file_path, char* find_name, struct variable* dest)
{
    char file_buffer[BUFF_SIZE] = { 0 }; // Buffer to store data
    FILE* stream = fopen(file_path, "r");
    if (NULL == stream)
    {
        return CANT_OPEN_FILE;
    }

    int error = 0;
    while (1)
    {
        // read type
        int read_type_result = read_line(file_buffer, BUFF_SIZE, dest->type, NAME_TYPE_SIZE, stream);
        if (read_type_result != 0)
        {
            error = read_type_result;
            break;
        }

        int read_name_result = read_line(file_buffer, BUFF_SIZE, dest->name, NAME_TYPE_SIZE, stream);

        if (read_name_result != 0)
        {
            error = read_name_result;
            break;
        }

        char value_buffer[VALUE_SIZE] = { 0 };
        int read_value_result = read_line(file_buffer, BUFF_SIZE, value_buffer, VALUE_SIZE, stream);
        if (read_value_result != 0)
        {
            error = read_value_result;
            break;
        }

        if (0 == strcmp(find_name, dest->name))
        {
            if (1 != sscanf(value_buffer, "%d", &dest->value))
            {
                error = CANT_FORMAT_VALUE;
            }
            break;
        }
    }

    fclose(stream);

    return error;
}

You just need to call the function find_var_in_file like in main. I loop over all the lines of the file and search for the var name. If have formating error or not find the name of the var in the file return the error code.

Answer 2

If the file you are trying to read is a text file (which it is in your case), then use fgets() to read its content. Also, if its content has a consistent format, then consider using sscanf() to do your parsing.

I don't understand why you are using a pointer to struct variable to save data. You can simply use a struct variable object and access its fields with .

Your code should look something like that:

#include <stdio.h>
#include <stdlib.h> // For exit()
#include <string.h> // for strlen()

struct variable {
    char type[10];
    char name[10];
    int value;
};

int main()
{
    FILE *file = fopen("input.txt", "r");
    if (!file) {
        fprintf(stderr, "Could not read file\n");
        return 1;
    }

    struct variable object2;
    char buffer[1024];

    while (fgets(buffer, 1024, file)) {
        if (sscanf(buffer, "%9s %9s %d", object2.type, object2.name, &object2.value) != 3) {
            fprintf(stderr, "Error parsing file\n");
            fclose(file);
            return 1;
        }

        printf("%s %s %d\n", object2.type, object2.name, object2.value);
    }

    fclose(file);
}

Now, if you want to store all the lines of your file into variables to use them later, then first you need to count the number of lines in your file (let's call it n) and second, allocate a dynamic array of size n.

Answer 3

fscanf(file,"%s\n%s\n%d\n",object2->type,object2->name,&object2->value);