out put the value from structure

Question

#include<stdio.h>

struct classifier
{
    char src_address[15];
    char dst_address[15];
    int src_port;
    int  dst_port;
};

main()
{
    int i;
    struct classifier clsf[4];
    struct classifier *ptr;

    for(i = 0; i < 2; i++)
    {
        ptr = & clsf[i];
        scanf("%s",ptr[i].src_address);
        scanf("%s",ptr[i].dst_address);
        scanf("%d",&ptr[i].src_port);
        scanf("%d",&ptr[i].dst_port);
        display(ptr[i]);
    }
}

void display(struct classifier ptr)
{
    printf("\n%s", ptr.src_address );
    printf("\n%s", ptr.dst_address );
    printf("\n%d", ptr.src_port);
    printf("\n%d", ptr.dst_port );
}

the o/p that i get is like this

this is i/p

123.123.123.123 
213.234.234.124
3244
1342

o/p
123.123.123.123213.234.234.124
213.234.234.124
3244
1342

why is that first value repeating. what is wrong in the code

What are you trying to do here? What output are you expecting? — Robert S. Barnes, Jan 17 '11 at 13:58

score 6 · Answer 1 · edited May 23 '17 at 11:55

Because you write too much data into your strings.

char src_address[15];

is 15 chars long, including the terminating 0 character, thus you must not put more than 14 characters into it. However, 123.123.123.123 is 15 chars.

Since the two fields src_address and dst_address happen to be stored in consecutive memory blocks, the value written into the latter follows immediately - without a separating 0 byte - the former. Thus printf cannot but print both when you intend to print the former.

You should reserve enough space in your char arrays to incorporate the terminating 0 value (and explicitly ensure that it really is put there!). In general, in real life apps you should defend yourself against buffer overruns caused by too long input.

out put the value from structure

1 Answers1