dynamic arrays

[floral cave]

initialized a dynamic array with nullptr.
assigned values to elements but trying to access those elements returns a segmentation fault

[chrome estuary]

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[lethal pilot]

How can one initialize a dynamic array with a nullptr.

;compile

#include <memory>
std::unique_ptr<int[]> darray(nullptr);

darray[0] = 0x100;

[charred junco]

Compiler Output

Program terminated with signal: SIGSEGV

__snape | 140ms | c++ | x86-64 gcc 14.2 | godbolt.org

[lethal pilot]

Is this what you did?

[floral cave]

used raw pointers

int* p = new int[5];
p = nullptr;
p[0] = 1;

[lethal pilot]

Well what else do you expect.

nullptr, Herald of Seg Faults

[floral cave]

i mean initializing a normal array with 0 then assigning a value let's you access the elements again

[steady atlas]

new int[5] returns a pointer to the beginning of the heap allocated memory that you binded to p, but then you reassigned THAT pointer object p to nullptr, this is wrong

[steady atlas]

hehe

[floral cave]

so I'm better off just initializing with 0

so when exactly is nullptr necessary

[steady atlas]

if you are using C++ don't use raw pointers for arrays, either use std::array if you know the size before-hand or an std::vector (if you want it to resize automatically as you add elements)

[steady atlas]

personally i will never recommend you to use nullptr in modern C++ now, if you want to indicate that a value might be absent then use an std::optional instead

this is a better practice

[lethal pilot]

nullptr the word is self explanatory, you use it when you want a pointer to hold no address.

[floral cave]

thx I'll look into that

[floral cave]

so one nullptr is used it can't hold an address during program flow again ?

[lethal pilot]

It can, you just reassign the pointer a new value.

[thorn rampart]

it can, nullptr is just a value that you assigned to a variable of pointer type

like any variable it can be reassigned

if the pointer points to memory that you don't have access to, like nullptr "does", and you try to access that memory anyway, like a pointer dereference or an array subscript do, segfaults are what you get

[lethal pilot]

I think you're misunderstanding the purpose of nullptr, when a pointer is not pointing to an object it has nullptr as it's value, you then assign it a valid value by giving it an address of an object.

[floral cave]

i think i get it now

[lethal pilot]

(it can have a garbage value I'm aware)

[floral cave]

thx

!solved

[chrome estuary]

Thank you and let us know if you have any more questions!

This thread is now set to auto-hide after an hour of inactivity

[steady atlas]

yeah it is indeterminate and dereferencing this pointer is an undefined behavior

[lethal pilot]

Your name has enough explaination 😆

[steady atlas]

true

[floral cave]

just gonna avoid using em

[steady atlas]

good 👍

[hasty coyote]

just to add my two cents: as others have said you should avoid manually allocating memory, there are smart pointers for that for 99% of cases

using raw pointers is OK as long as you know what you're doing

and the modern way to use arrays in C++ is through std::array

[oak cairn]

std::array requires a complie time constant, this question is about dynamic arrays ...

[hasty coyote]

my bad

[steady atlas]

i mentioned both here

hmmmm my wording is a bit wrong though, should have said that the size must be a "compile time constant" rather than "know the size beforehand"