Moving pointer in array

Question

This program crashes and I can't find any nonlegal action regarding getting array content and moving pointer. What is wrong?

#include <iostream>
#include <stdint.h>
using namespace std;


int main( int argc, char ** argv ) {


    int * p =  new int [20];
    for(int i=0 ; i<20 ;i++ )
        {
            p[i]=i;
        }

    for(int i=0 ; i<20 ;i++ )
        {
            printf("%d ",*p );
            p++;
        }


    delete [] p;

    return 0;
}

Question: Why are you using new in the first place? You're going through a lot of extra gyration to get pretty much the result you'd get from just making p an array/std::vector/std::array local to main. You've gotten lots of advice about how to keep the new/delete from crashing, but none that points out that you shouldn't be using them to start with (and even when you need new-like capabilities, you should look at make_shared and make_unique instead of using new directly). — Jerry Coffin
– Jerry Coffin, Commented Nov 25, 2013 at 17:03
@JerryCoffin let me answer that - mostly because majority of C++ books, resources, courses (even the University ones) still prefer to show how to implement linked list in C and then to compile it with C++ compiler. People are still teaching other people how to feel comfortable inside "C ghetto" (as Bartosz Milewski named it). — Nemanja Boric
– Nemanja Boric, Commented Nov 25, 2013 at 17:12

Nemanja Boric · Accepted Answer · 2013-11-25 17:00:10Z

6

You're changing your p pointer, and then you're trying to delete memory after the original allocated memory:

delete [] p;

Save the the original pointer to some temporary iterator pointer and increment it, and not the original one:

    int *t = p;
    for(int i=0 ; i<20 ;i++ )
    {
        printf("%d ",*t );
        t++;
    }

answered Nov 25, 2013 at 17:00

Nemanja Boric

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gt6989b · Accepted Answer · 2013-11-25 17:01:05Z

2

You are deleting a pointer pointing to the next element after your memory block.

answered Nov 25, 2013 at 17:01

gt6989b

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Comments

Dejan · Accepted Answer · 2013-11-25 17:01:08Z

2

Save starting pointer of array in another pointer and delete that old pointer on the end.

answered Nov 25, 2013 at 17:01

Dejan

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