CODEWITHSUNDEEP
cstructure
asir
asir

Reputation: 13381

passing the structure to function

when is do this i get

error: incompatible type for argument 1 of ‘display’ 

    #define M 4
    struct show
    {
     int value;
    };

    struct node
    {
     struct show keys[M-1];
    };

    void display(struct show *ptr)

    main()
    {
                struct show key;
                printf("Enter value:\n ");
                scanf("%d",&keys.value);
                display(keys);

    }

    void display(struct show *ptr)
    {

     printf("%d", ptr->value);

    }

but when i give display(&key) there wont be any error, but when i pass keys as parameter to display it is like passing the address of the structure itself, why should i give &keys?

Upvotes: 0

Views: 1050

Answers (5)

Victor Nicollet
Victor Nicollet

Reputation: 24587

keys is a structure, but display expects a pointer to a structure (you wrote * for that purpose). Using display(&keys) passes a pointer to the structure instead.

The point of passing a pointer instead of a structure is that C arguments are passed by value, which involves a copy. If you passed the structure, then a copy would be made which, given that a structure is usually pretty large, is an unnecessary waste of processing time. Passing a pointer involves only a copy of that pointer, which is faster.

Upvotes: 1

badgerr
badgerr

Reputation: 7982

It's tricky to tell what you're trying to do, but as far as compilation errors go, where you have written this:

scanf("%d",&keys.value);
display(keys);

I think you mean to write this:

scanf("%d",&key.value);
display(&key);

Upvotes: 2

Hertzel Guinness
Hertzel Guinness

Reputation: 5950

i think you meant this:

#include <stdio.h>

#define M 4
struct show
{
    int value;
};

struct node
{
    struct show keys[M-1];
};

void display(struct show *ptr);

main()
{
    int i;
    struct node node_instance;
    for (i = 0; i < M-1; i++) {
        printf("Enter value #%d:\n ", i);
        scanf("%d",&node_instance.keys[i].value);
        display(&node_instance.keys);
    }

}

void display(struct show *ptr)
{
    printf("%d\n", ptr->value);
}

Upvotes: 0

Simone
Simone

Reputation: 11797

You have to create a variable of struct node type and pass its keys address.

main()
{
    struct node theNode;
    // populate theNode's keys elements
    display(theNode.keys);
}

Anyway, with the given code you will only print the first element of keys collection, so you will need to update display() function (i.e.: you will have to pass in the number of elements in keys array).

Upvotes: 0

user82238
user82238

Reputation:

You're missing a semi-colon at the end of the prototype for display().

Also you need to indicate the return type from main, e.g. void main().

Upvotes: 0

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