Add string to array C (pointers)

Question

Hello everyone here below i have some code that intialisize an array with 4 elements but there is space for 50 elements.

Now i want that i can manually add some elements to the array but it doesn't work for me can somebody help me? like here i want to add Sander to the 5th element.

#include <stdio.h>

int main()
{
    int i;

char *arr[50] = {"C","C++","Java","VBA"};
char *(*ptr)[50] = &arr;

(*ptr)[5]="Sander";
for(i=0;i<5;i++)
    printf("String %d : %s\n",i+1,(*ptr)[i]);

return 0;
}

Thx a lot

Probably because the fifth element is at (*ptr)[4] :) Remember that array indexing is zero-based. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Mar 14, 2017 at 20:19
I have one more question how i can i get the lengt of the indexes that arre used i tried it already with sizeof but that wasn't correct — Sandeerius
– Sandeerius, Commented Mar 14, 2017 at 20:26
If you have another question, post another question, not a comment. This is a Q&A site, so use its facilities. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Mar 14, 2017 at 20:27

Vlad from Moscow · Accepted Answer · 2017-03-14 20:25:28Z

8

It seems you mean the following

#include <stdio.h>

int main( void )
{
    int i;

    char *arr[50] = {"C","C++","Java","VBA"};
    char **ptr = arr;

    ptr[4] = "Sander";

    for ( i = 0; i < 5; i++ )
        printf("String %d : %s\n", i+1, ptr[i] );

    return 0;
}

Or the following

#include <stdio.h>

int main( void )
{
    int i;

    char *arr[50] = {"C","C++","Java","VBA"};
    char * ( *ptr )[50] = &arr;

    ( *ptr )[4] = "Sander";

    for ( i = 0; i < 5; i++ )
        printf("String %d : %s\n", i+1, ( *ptr )[i] );

    return 0;
}

In the both cases the output will be

String 1 : C
String 2 : C++
String 3 : Java
String 4 : VBA
String 5 : Sander

answered Mar 14, 2017 at 20:25

Vlad from Moscow

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6 Comments

aerijman Over a year ago

what happen with the other 45 slots of memory? Where they allocated (is there such a thing in the stack?).

Vlad from Moscow Over a year ago

@aerijman The array is allocated in the stack, It is an array of pointers that point to string literals that have static storage duration. The elements of the array that were not initialized explicitly are implicitly set to NULL.

aerijman Over a year ago

then NULL elements do not occupy memory?

Vlad from Moscow Over a year ago

@aerijman The array has 50 elements that occupy an extent of a memory in the stack. The size of the extent is equal to 50 * sizeof( char * ). Only the first 4 elements are initialized by addresses of string literals while others are initialized by zeroes.

aerijman Over a year ago

Given char *arr[] = {"C","C++","Java","VBA"};, what's the problem with arr[4] = "Sander";?

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