Add an adress to an array of pointers C

Question

I have to write a function that will add an adress at the end of an array of pointers. Here is what I've done. I want to know if I did right and if not, please correct me.

#include <stdio.h>
#include <stdlib.h>
#define MAX 3

void add( int *array[MAX], int *addr)
{
    array = realloc(array, 1*sizeof(int));
    array[MAX+1] = addr;
}

int main()
{
    int *addr = 4;
    int *array[MAX] = {"1","2","3"};
    add(array, addr);
    int i;
    for(i = 0; i<4;i++)
        printf("%d ", array[i]);

    return 0;
}

Yes, it gives me 4 addreses, but I'm not sure if the fourth adress is the adress that i passed or just a random address. — Vlad Dohotaru, Aug 30 '15 at 08:08
Which `c` compiler are you using ? because when i tried it on ideone.com it gives Runtime error : http://ideone.com/2QVeNu — surajs1n, Aug 30 '15 at 08:16
I've compiled it on tutorialspoint.com and it gives just some warnings — Vlad Dohotaru, Aug 30 '15 at 08:19
If you already tried, then you should notice 1) you cannot assign a pointer `addr` to `int`, 2) you cannot assign an `array` of pointers to `int` that way. — artm, Aug 30 '15 at 08:27
`array = realloc(array, 1*sizeof(int));` does either nothing useful (since the pointer is passed by value), or invokes UB (if you pass it a pointer that wasn't allocated by `malloc()`/`calloc()`). — The Paramagnetic Croissant, Aug 30 '15 at 08:40

Itay Sela · Accepted Answer · 2015-08-31T10:15:12.917

from the manual for realloc:

The realloc() function changes the size of the memory block pointed to by ptr to size bytes. The contents will be unchanged in the range from the start of the region up to the minimum of the old and new sizes. If the new size is larger than the old size, the added memory will not be initialized. If ptr is NULL, then the call is equivalent to malloc(size), for all values of size; if size is equal to zero, and ptr is not NULL, then the call is equivalent to free(ptr). Unless ptr is NULL, it must have been returned by an earlier call to malloc(), calloc() or realloc(). If the area pointed to was moved, a free(ptr) is done.

if its too long to read ill explain.

first of all you should use realloc after allocating memory ( using malloc for example ) and not after local declaration

second you're treating pointers to int ( int * ) as if they we're int. also shown as warning

examples:

int *addr = 4; 
int *array[MAX] = {"1","2","3"}; 
array = realloc(array, 1*sizeof(int));     // here you're using sizeof( int )

another problem is reaching out of bound of array

 array[MAX+1] = addr;

for an array with 3 spaces - you have array[ 0 ], array[ 1 ] and array[ 2 ].

in this line you're trying to reach the array[ 4 ] of an array ( that's suppose to be ) of size 4 --> out of bounds

my suggested code for this will be:

code edited

#include <stdio.h>
#include <stdlib.h>
#define MAX 3

void add( int **array[ MAX ], int *addr )
{
    *array = realloc( *array, ( MAX + 1 ) * sizeof( int* ) );
    (*array)[ MAX ] = addr;
}

int main()
{
    int i;
    int *addr;
    int **array;

    addr = &i;
    array = malloc( MAX * sizeof ( int* ) );
    for ( i = 1; i <= MAX; i++ ) {
        array[ i - 1 ] = addr + 4 * i;
    }

    add( &array, addr );

    for ( i = 0; i < MAX + 1; i++ ) {
        printf( "%p ", array[ i ] );
    }

    return 0;
}

I understood,thank you. But, my task says that my function add should add an address to this array of pointers. Your function seems to add the value. And will the same work with strings? For example, If I want to add a string address to an array of pointers? — Vlad Dohotaru, Aug 30 '15 at 08:57
This is still not completely correct. The `add` function will not change the array that was passed in to it, it only changes its local variable `array`. — interjay, Aug 30 '15 at 09:33

Add an adress to an array of pointers C

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