Passing an array of pointer's value to a file in c

Question

I'm using an array of pointers to pass the inputted values to a text file but when I use fputs I keep getting the error "expected const char*", and as the array of pointers is defined from the struct named books it is of the type "struct books *". I tried using the puts statement but that doesn't solve the problem either. Would it be better not to use pointers?

const char *BOOKS = "books.txt";

struct Books{
int isbn;
char title[25];
char author[20];
char status[10];
}*a[MAX];

int main (void)
{
int i;
printf("Enter the books details that you currently have:\n\n");

for(i=0;i<MAX;i++)
{
    printf("Enter the book's isbn number:");
    scanf("%d", &a[i]->isbn);

    printf("Enter the book's title :");
    scanf("%s", &a[i]->title);

    printf("Enter the book's author:");
    scanf("%s", &a[i]->author);

    printf("Enter the book's status, whether you 'have' or whether it is      'borrowed':");
    scanf("%s", &a[i]->status);
}

FILE *fp = fopen(BOOKS,  "r+" );        
if (fp == NULL )        
{
    perror ("Error opening the file");
}
else    
{
    while(i<MAX  )  
    {
        fputs( a[i]->status, fp);
        fputs(a[i]->author, fp);
        fputs( a[i]->title, fp);
        fputs( a[i]->isbn, fp);
    }
    fclose (fp);    
}
}

Storing a pointer in a file is almost always a very bad idea. — too honest for this site
– too honest for this site, Commented Mar 13, 2016 at 18:03
You made an array of pointers to Book, but you did not make them point anywhere yet. Writing a[i]->isbn dereferences a null pointer. It would be simpler to use an array of Book instead . — M.M
– M.M, Commented Mar 13, 2016 at 22:26

Sudipta Kumar Sahoo · Accepted Answer · 2016-03-13 18:22:44Z

1

Assuming you have not given the complete code, So far I understand you want to write the structure elements to the FILE you have opened. In your for loop you need to use fputs some thing as follow,

fputs(a[i].title, fp);
fputs(a[i].author, fp);
fputs(a[i].status, fp);

Then it should work with out any error. Hope That Helps.

answered Mar 13, 2016 at 18:22

Sudipta Kumar Sahoo

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2 Comments

sc100 Over a year ago

I just tried this and I am still getting the same error. And yes, you're write, I do want to write the structure elements to the file I've opened.

Sudipta Kumar Sahoo Over a year ago

@sc100 I have added an answer by modifying your code. Please have a look. If it works verify it by accepting to help others.

Sudipta Kumar Sahoo · Accepted Answer · 2016-03-13 19:13:33Z

0

Hi I have modified your program as follow, Please have a look,

const char *BOOKS = "books.txt";
struct Books{
int isbn;
char title[25];
char author[20];
char status[10];
}a[MAX];

int main (void)
{
    int i;
    char *ISBN;
    printf("Enter the books details that you currently have:\n\n");

    for(i=0;i<MAX;i++)
    {
        printf("Enter the book's isbn number:");
        scanf("%d", &a[i].isbn);

        printf("Enter the book's title :");
        scanf("%s", &a[i].title);

        printf("Enter the book's author:");
        scanf("%s", &a[i].author);

        printf("Enter the book's status, whether you 'have' or whether it is      'borrowed':");
        scanf("%s", &a[i].status);
    }

    i = 0;

    FILE *fp = fopen(BOOKS,  "r+" );
    if (fp == NULL )
    {
        perror ("Error opening the file");
    }
    else
    {
        while(i<MAX  )
        {
            fputs( a[i].status, fp);
            fputs(a[i].author, fp);
            fputs( a[i].title, fp);
            itoa(a[i].isbn,ISBN,10); // Convert the isbn no to const char* in decimal format. to write in to the file.
            fputs( ISBN, fp);
            i++;   //Increment 'i' to access all the elements
        }
        fclose (fp);
    }
    return 0;
}

Hope this Helps.

answered Mar 13, 2016 at 19:13

Sudipta Kumar Sahoo

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1 Comment

M.M Over a year ago

You should explain what changes you made and why

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