Ways to initialize RAII

Asked Nov 13 '20 at 19:13

Active Nov 13 '20 at 19:23

Viewed 73 times

I'm curious, what is the difference between this:

std::unique_ptr<char> ptr = std::unique_ptr<char>(new char[1000]);

and this:

std::unique_ptr<char> ptr(new char[1000]);

Also, this is unrelated, but how can I use make_unique for an array without initializing the values?

edited Nov 13 '20 at 19:22

asked Nov 13 '20 at 19:13

ManUser123

Neither is legal, ITYM `std::unique_ptr` – john Nov 13 '20 at 19:15
1

It is an array to use `std::unique_ptr` to hold a `char` array. Use `std::vector` or `std::unique_ptr`. Please read [Proper way to create unique_ptr that holds an allocated array](https://stackoverflow.com/questions/21377360/proper-way-to-create-unique-ptr-that-holds-an-allocated-array). – François Andrieux Nov 13 '20 at 19:16
@john but it compiles and works. – Suthiro Nov 13 '20 at 19:17
That wasn't my question. My question was what is the difference between init an object like this: `Object obj(params)` and this: `Object obj = Object(params)` – ManUser123 Nov 13 '20 at 19:17
C++20 introduces `std::make_unique_for_overwrite` which default initializes the object. I believe for `char[]` this would mean not initializing its elements. – François Andrieux Nov 13 '20 at 19:17
@ManUser123 So you not specifically interested in unique_ptr? – john Nov 13 '20 at 19:17
@john No. I'm just curious at the differences between those 2 init methods – ManUser123 Nov 13 '20 at 19:18
2

@Suthiro It compiles and it works does not guarantee that it is correct. – john Nov 13 '20 at 19:18
@Suthiro Compiling and looking like it works does not make it correct. This version is equivalent to using `delete` instead of `delete[]` for an array. It is Undefined Behavior. – François Andrieux Nov 13 '20 at 19:18
@ManUser123 Probably should have picked a made up type to illustrate the question then. – john Nov 13 '20 at 19:19
@john Yeah. Now I have to wait 90 minutes :( – ManUser123 Nov 13 '20 at 19:19
@ManUser123 Then is the last sentence of your question entirely unrelated to the rest of the question? – François Andrieux Nov 13 '20 at 19:20
@FrançoisAndrieux you are right, now I see. – Suthiro Nov 13 '20 at 19:20
@ManUser123 I'm sure this has been asked before, I see if I can find a duplicate. – john Nov 13 '20 at 19:20
@FrançoisAndrieux Yeah, the last sentence was unrelated. My bad. – ManUser123 Nov 13 '20 at 19:20
1

@ManUser123 Found a reasonable duplicate for part 1. – john Nov 13 '20 at 19:23
@john Thanks! I'll check it out – ManUser123 Nov 13 '20 at 19:25

Ways to initialize RAII

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