How to use array of pointers to print structure entities?

Question

I wrote a program in C which has a structure named ak. There is an array of pointers s which stores the address of array p of ak type. After inputting the values, only str is getting printed.

How can I print both str and id using array of pointers?

set 1:

#include<stdio.h>
typedef struct
{
    char str[10];
    int id;
}ak;

int main()
{   
    printf("Hey\n"); 
    int i;
    ak *s[5],p[5];
    for(i=0;i<5;i++)
    {
        s[i]=&p[i];
        printf("Input string:");
        scanf("%s",&p[i].str);
        printf("Input id:");
        scanf("%d",&p[i].id);
    }    
    i=0;
    while(i<5)
    {
        printf("%s\n",s[i].id);
        ++i;
    } 
    return 0;   
}

set 2:

#include<stdio.h>
typedef struct
{
    char str[10];
    int id;
}ak;

int main()
{  
    printf("Hey\n"); 
    int i;
    ak *s[5],p[5];
    for(i=0;i<5;i++)
    {
         s[i]=&p[i];
         printf("Input string:");
         scanf("%s",&p[i].str);
         printf("Input id:");
         scanf("%d",&p[i].id);
    }    
    i=0;
    while(i<5)
    {
         printf("%s\n",s[i]);
         ++i;
    }
    return 0;    
}

So when I tried set1 code,it gave me error saying:

C:\CPP\c\Prototypes>gcc -o ct structure.c
structure.c: In function 'main':
structure.c:22:32: error: request for member 'id' in something not a structure or union

       printf("%s\n",*s[i].id);
                          ^

Screenshot is here:

https://imageshack.com/a/img921/3084/j1rHig.png

When I tried set2 code, it only printed str values. screenshot is here:

https://imageshack.com/a/img922/614/JHSGZ9.png

The error message means you’re using the dot operator where you should be using the arrow operator, or vice versa. — Jonathan Leffler
– Jonathan Leffler, Commented Jan 1, 2019 at 14:49
Please use Copy&Paste to show us the text error messages. They are no artwork and don't need to be shown as images. — Gerhardh
– Gerhardh, Commented Jan 1, 2019 at 18:21
the set1 does not compile. How are we to advise you on run-time logic when you do not post code that compiles? — user3629249
– user3629249, Commented Jan 2, 2019 at 0:53
the set2 results in the compiler giving two (serious) warnings: untitled.c:17:18: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[10]’ [-Wformat=] and untitled.c:24:19: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘ak * {aka struct <anonymous> *}’ [-Wformat=] Both of these problems need to be corrected, or the code will not act as desired when run — user3629249
– user3629249, Commented Jan 2, 2019 at 0:56
OT: the struct definition is missing a 'tag' name. Without a 'tag' name, most debuggers will not display the individual fields in the struct. — user3629249
– user3629249, Commented Jan 2, 2019 at 0:59

bruno · Accepted Answer · 2019-01-02 06:13:07Z

2

Concerning set1 and your problems with printf("%s\n",*s[i].id);.

*s[i].id is equivalent to *(s[i].id), not to (*s[i]).id as you probably supposed. Because the type of s[i] is ak * you cannot get its field id through s[i].id.

You can write (*s[i]).id but a more readable way is to use s[i]->id.

Your printf has an other problem, the format cannot be "%s" because s[i]->id is an int, not a char *

Concerning set2

You do printf("%s\n",s[i]);, and you are surprised because only the string is printed, how can you expect that print the string and the int ?

You request to print a string (format %s) but s[i] is not a string. By chance the struct starts by the field str being a string, so yes you write it, but this is not the right way.

You have to explicitly print each attributes, for instance doing printf("%s %d\n",s[i]->str, s[i]->id);

edited Jan 2, 2019 at 6:13

answered Jan 1, 2019 at 10:25

bruno

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1 Comment

bruno Over a year ago

@AthulKrishnan do you understand the problems ?

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