How do I shift elements down in an array of string of struct? [duplicate]

Question

Given an array of a struct with several elements, I would like to delete, say element 2, and want the elements 3,4,5.. to shift to 2,3,4.

In my code below, the add and delete functions work fine. I have tried with strcpy() function but it didn't work.

    struct Books {
        char title[20];
        char author[20];
    };

void add_book(struct Books book1[], int *counter){

    fflush(stdin);
    printf("Title: ");
    gets(book1[*counter].title);
    printf("Author: ");
    gets(book1[*counter].author);
    *counter++;

    return;
}

void delete_book(struct Books book1[], int *counter){

    int i = 0;
    int delete = 0;
    printf("What nr of book you want to delete: ");
    scanf("%d", &delete);

    book1[delete-1].title[0] = '\0';
    book1[delete-1].author[0] = '\0';
    *counter--;

    /*
     here I want to move elements down one step if I delete for example one 
     element in the middle
    */
    return;
}

int main(){

    struct Books book1[50];
    int count = 0; //for keeping track of how many books in the register

    add_book(book1, &count);
    delete_book(book1, &count);

    return 0;
}

memmove is a very good function to move (overlapping) data around in memory. — Some programmer dude
– Some programmer dude, Commented Oct 8, 2017 at 16:44
Also note that falling fflush and passing an input-only stream (like stdin) is explicitly mentioned as undefined behavior by the C specification. Some standard library implementations have added it as an extension, but please try to avoid it. — Some programmer dude
– Some programmer dude, Commented Oct 8, 2017 at 16:45
this question is already answered here stackoverflow.com/questions/15821123/… — Ahmed Masud
– Ahmed Masud, Commented Oct 8, 2017 at 16:48
I only used fflush because the add_book function didnt work without it — Bei
– Bei, Commented Oct 8, 2017 at 16:49

Paul Ogilvie · Accepted Answer · 2017-10-08 17:06:08Z

0

At the point where your comments says you want to move the remaining books down, add:

    memmove(&book1[delete-1],  &book1[delete], (*counter-delete)*sizeof(struct Books);
    *counter--;  // better to decrement it here

^{(Not tested)}

answered Oct 8, 2017 at 17:06

Paul Ogilvie

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3 Comments

Bei Over a year ago

It almost worked. I added 3 books, and then deleted the first element, the second element moved to the first element, but the third was copied to the second so element 2 and 3 contained same value

Paul Ogilvie Over a year ago

Yes, and when you delete an element, there is one less. counter says how many elements there are. Any element from counter and higher "does not exist" so their values are not important.

Bei Over a year ago

Ok it seems to work, if I use (*counter)--;

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