C Struct Array Input

Question

I have the following struct

typedef char String[256];

typedef struct
{
    String name;
    int year;
    float price;
} Book;

Array of Books

int main(int argc, const char * argv[])
{    
    Book books[5];

    for (int i=0; i<5; i++) {
        books[i] = inputBook();
    }

    return 0;
}

inputBook() function

Book inputBook()
{
    Book myBook;

    //Name
    puts("Enter Book Name:");
    gets(myBook.name);

    //Publishing Year
    puts("Enter Book Publishing Year:");
    scanf("%i", &myBook.year);

    //Price
    puts("Enter Book Price:");
    scanf("%f", &myBook.price);

    return myBook;
}

For some reason the first book input is going well but when trying to input the second book and the second call to inputBook() I can set a book name, it jumps straight to the year import.

What is the problem ?

Thanks!

I think you forget to count byte of the new data. If byte of new data < reserved place, it will happen — , Jul 12 '12 at 11:01
Forgive me, type error not "<", correct one ">" . Correct sentence will be " If byte of new data > reserved place, it will happen" — , Jul 12 '12 at 11:11

score 4 · Accepted Answer · edited May 23 '17 at 12:12

4

To correct, replace:

gets(myBook.name);

with:

scanf("%255s", myBook.name); /* 255 as name is 256 chars. */

as scanf() will skip any whitespace characters, but gets() will not. A newline character is considered a whitespace character and there will be a newline remaining in stdin after the price has been entered causing gets() to read the newline and effectively read nothing.

Worth reading: warning:gets function is dangerous

edited May 23 '17 at 12:12

Community

1
1

answered Jul 12 '12 at 11:06

hmjd

120,187
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but `scanf("%255s", myBook.name);` doesn't scan multiple words. see [here](http://stackoverflow.com/questions/19379141/c-multiple-words-input-using-scanf) – mrudult Oct 15 '13 at 10:51

score 1 · Answer 2 · answered Jul 12 '12 at 10:58

This is because the variable myBook is valid only in the inputBook scope and is destroyed as soon as the function exits.

you should pass the book item you want to initialize as a parameter of your function.

function inputBook()...

void inputBook(Book *ptBook )
{
    if( ptBook==NULL )
        return;

    //Name
    puts("Enter Book Name:");
    gets(ptBook->name);

    //Publishing Year
    puts("Enter Book Publishing Year:");
    scanf("%i", &ptBook->year);

    //Price
    puts("Enter Book Price:");
    scanf("%f", &ptBook->price);
}

The main function...

int main(int argc, const char * argv[])
{    
    Book books[5];

    for (int i=0; i<5; i++) {
        inputBook( &books[i] );
    }

    return 0;
}

But the return value is being copied, no? Which is ok (http://stackoverflow.com/questions/2302351/assign-one-struct-to-another-in-c). — hmjd, Jul 12 '12 at 11:11
It depends on the compiler...e.g. SDCC does not support this feature. http://sourceforge.net/apps/trac/sdcc/wiki/Standard%20compliance — A.G., Jul 12 '12 at 11:25

score 1 · Answer 3 · answered Jul 12 '12 at 11:04

1

I think you need to flush stdin before next iteration. You have orevious CRLF in your stdin stream.

use fflush(stdin); in the beginning of loop.

answered Jul 12 '12 at 11:04

DexTer

2,043
1
22
45

score 0 · Answer 4 · answered Jul 12 '12 at 10:57

0

Maybe you can try fflush(stdin) before input.

Book inputBook()
{
    Book myBook;

    fflush(stdin);

    // rest of the code
}

answered Jul 12 '12 at 10:57

Rango

1,087
7
5

1

Flushing `stdin` is undefined behavior AFAIK. `fflush` is generally intended for output streams. – Pavan Manjunath Jul 12 '12 at 10:58
@PavanManjunath To avoid using fflush(stdin), one can write a short func to read all bytes in stdin. That solves the problem too. – Rango Jul 12 '12 at 11:01

score 0 · Answer 5 · answered Jul 12 '12 at 12:10

#include <stdio.h>

typedef char String[256];

typedef struct
{
    String name;
    int year;
    float price;
    } Book;
Book inputBook()
{
    Book myBook;

    //Name
    puts("Enter Book Name:");
    getchar();
    gets(myBook.name);

    //Publishing Year
    puts("Enter Book Publishing Year:");
    scanf("%i", &myBook.year);

    //Price
    puts("Enter Book Price:");
    scanf("%f", &myBook.price);

    return myBook;
}
int main(int argc, const char * argv[])
{
    Book books[5];

int i = 0; for (i=0; i<5; i++) {
    books[i] = inputBook();
}

return 0;
}

at the usage of fflush(stdin): i have point to make.. ! you can also use, fgetc.. as well as if you are using gcc.. fflush might not be supporting.. — Ashutosh, Jul 12 '12 at 12:25

C Struct Array Input

5 Answers5