How to remove an element from a new array

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I have an array allocated like so

C++

ClassName *var = new ClassName [NumItems];

I delete it using

C++

delete [] var;

Currently when a single item is removed I call memmove to shift everything over, but that causes delete to throw an exception when debugging. (Been shipping it this way for a decade, customers rarely use it)

C++

memmove(&var[index], &var[index + 1], sizeof(ClassName) * (NumItems - (Index + 1));

How do you properly remove an item in the middle of an array allocated this way?

I do not want to change it to an array class because I would have to change 100+ functions and do not want to spend that much time. I am just curious as to how to do it this way correctly.

What I have tried:

memmove as specified in the above explanation

Posted 30-Jun-22 12:00pm

RandyS

Updated 2-Jul-22 10:49am

CPallini

v2

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Daniel Pfeffer · Answer 1 · 2022-07-02T10:49:00

The C++ library is your friend here:

C++

Class* arrayOfClass = new arrayOfClass[N];

// fill array code skipped

// delete element n of the array, leaving element N-1 in a destructible state
std::move(arrayOfClass + n, arrayOfClass + (n + 1), arrayOfClass + N);

// the only things that you may do with element N-1 are:
//   assign a new value to it
//   destruct it (e.g. when the entire array is destructed)

merano99 · Answer 2 · 2022-07-01T08:24:00

Solution 3

Quote:
Currently when a single item is removed I call memmove to shift everything over,..

Why use an array when you want to delete elements in it?
Wouldn't a vector be a better idea?

Posted 1-Jul-22 8:24am

merano99

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CPallini 1-Jul-22 16:06pm

Possibly because "I do not want to change it to an array class because I would have to change 100+ functions and do not want to spend that much time. I am just curious as to how to do it this way correctly"?
:-D

merano99 1-Jul-22 20:28pm

Yes, possibly. I don't know why anyone would have to change more than 100 functions either:-D

CPallini · Answer 3 · 2022-06-30T20:48:00

Solution 2

See this page: c++ - Will memcpy or memmove cause problems copying classes? - Stack Overflow[^].

Posted 30-Jun-22 20:48pm

CPallini

steveb · Answer 4 · 2022-06-30T20:44:00

Solution 1

Given your code above it should look like this:

C++

size_t bytes_to_move = NumItems - index + 1;
memmove(var + index, var + index + NumItems, bytes_to_move* sizeof(ClassName));

Posted 30-Jun-22 20:44pm

steveb

Updated 30-Jun-22 20:56pm

v3