Question

How can I read a long integer with 12 or 13 digits (like a ISBN number of a book) in C? I want to read the number from a text file with information of books(ISBN/name/writer).

The content of the text file is like this:

0393312836

A Clockwork Orange

Anthony Burgess

0199536759

Middlemarch

Bret Easton Ellis

…

…

…

and I am using this code:

int main(void){

    FILE *f;
    char name[MAX], writer[MAX], line[MAX];
    long isbn;

    f=fopen("path.txt","r");
    if(f == NULL){
        return 0;
        }

    while (fgets(line, 1024, f) != NULL){

        sscanf(line,"%ld", &isbn);
        printf("ISBN: %ld\n",isbn);

        fgets(nome, 1024, f);
        printf("NAME: %s",name);

        fgets(line, 1024, f);
        printf("WRITER: %s",writer);


        }
    fclose(f);

    return 0;

}

he is able to read the names of the books and the writers, but he only reads the numbers if they have 9 digits or less. what do I have to do to make this work?

Answer 1

I think for an ISBN you would be much better using a string. You won’t need to perform arithmetic on the value, you can store leading zeroes and you’ll want a string to store the X that you can get in an ISBN 10 checksum.