Re: "Linus Torvalds Was (Sorta) Wrong About C++"

From:

BGB <cr88192@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 11 Mar 2015 20:34:12 -0500

Message-ID:

<mdqqks$4ms$1@news.albasani.net>

On 3/11/2015 4:41 PM, JiiPee wrote:

On 11/03/2015 21:29, Mr Flibble wrote:

On 11/03/2015 21:15, Paavo Helde wrote:

JiiPee <no@notvalid.com> wrote in news:Ie1Mw.381530$dX1.143786@fx21.am4:

int size = 10;
int* a = new int[size ];
float* b = new float[size ];
double* c = new double[size ];

This is not exactly equivalent to std::vector because the capacity and
efficient dynamic resizing are missing.

so in C we need total : 4 bytes overhead

16 bytes, if you want to compare correctly. Each pointer is an overhead.
And if you add capacities, it will make 28 bytes.

in C++:
vector<int> a = ...10);
vector<float> b = ...10);
vector<double> c = ..10).;

would need total: 36 bytes of overhead

If the vectors are always of the same length, then the solution is
clear:

struct X {
         int a;
         float b;
         double c;
};

std::vector<X> x;

Voila: this has 12 bytes overhead, which is 4 bytes less than the C
version, plus it supports efficient dynamic resizing as a bonus, plus it
is not error-prone and exception-unsafe - an even bigger bonus. Q.E.D.

You could of course have a dynamic array of X also.

In my most humble opinion dynamic arrays should only be used for one
thing: allocating uninitialised buffers of char; use std::vector for
everything else..

/Flibble

but the issue here is using as little RAM memory as possible

yeah.

for example, if writing code for microcontrollers, these don't really
have an abundance of RAM. a higher-end microcontroller may have
double-digit kB of RAM, but many have only single-digit kB, and some
don't even have kB (you get maybe 256 or 512 bytes of RAM and maybe a
few kB of ROM).

granted, ARM SoCs tend to be a lot more powerful, but there are few good
options if one wants something fairly cheap and available in DIP
packages (vs QFP or BGA or similar).

or such...