Passing an array from a struct as an argument to a function

Question

#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct
{
    int votes;
}
candidate;

void array_function(int arr[]);

int main(void)
{
    candidate candidates[3];
    candidates[0].votes = 5;
    candidates[1].votes = 3;
    candidates[2].votes= 1;
    print_array_function(candidates.votes);
}

void print_array_function(int arr[])
{
    for (int i = 0; i < 3; i++)
    {
        printf("%i\n", arr[i]);
    }
}

I'm trying to run this code which declares a struct, feeds values into it and tries to pass an array inside the struct to a function. However, on doing so I get the following error:

test.c:22:30: error: member reference base type 'candidate [3]' is not a structure or union
    array_function(candidates.votes);

How do I pass this structs array into the function?

Your struct *does not contain* an array. You can’t just treat the members of structs inside an array as an array of values. The error message says exactly that: `candidates` is of type *array* (more precisely, `candidate[3]`), it is *not* a struct type. — Konrad Rudolph, Jul 30 '20 at 07:43

score 0 · Accepted Answer · answered Jul 30 '20 at 07:45

0

Just declare the function like

void array_function( const candidate arr[], size_t n );

and call like

print_array_function( candidates, 3 );

The function can be defined the following way

void array_function( const candidate arr[], size_t n )
{
    for ( size_t i = 0; i < n; i++ )
    {
        printf( "%i\n", arr[i].votes );
    }
}

answered Jul 30 '20 at 07:45

Vlad from Moscow

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Is it possible to send only candidates.vote instead of the entire struct? – Zohair Ul Hasan Jul 30 '20 at 07:49
@ZohairUlHasan Why are you trying to write an obfuscated code? In general it can be incorrect because the alignment of the structure can be specified differently. – Vlad from Moscow Jul 30 '20 at 08:00

score 0 · Answer 2 · answered Jul 30 '20 at 07:50

Here, you have an array of structure candidate which each element contains a single int called votes (certainly vote would be a better name for it). Maybe the best approach to do what you want is to create a function print_candidate_array_vote as :

void print_candidate_array_vote(candidate *candidates, unsigned int n_candidates)
{
    for (int i = 0; i < n_candidates; i++) {
        printf("%d\n", candidates[i].votes);
    }
}

score 0 · Answer 3 · answered Jul 30 '20 at 07:55

Try the code below, have made some changes

 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>

 typedef struct candidate
 {
 int votes;
 }
candidate;

void array_function(int arr[]);

int main(void)
{
    candidate candidates[3];
    candidates[0].votes = 5;
    candidates[1].votes = 3;
    candidates[2].votes= 1;
    print_array_function(candidates);
}

void print_array_function(candidate arr[])
{
   for (int i = 0; i < 3; i++)
   {
       printf("%i\n", arr[i]);
   }
}

Passing an array from a struct as an argument to a function

3 Answers3