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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: initial size of a std::vector of std::strings
Date: Wed, 07 Dec 2022 14:53:39 -0800
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Lynn McGuire <lynnmcguire5@gmail.com> writes:
> On 12/7/2022 2:23 AM, Öö Tiib wrote:
>> On Wednesday, 7 December 2022 at 07:42:49 UTC+2, Lynn McGuire wrote:
>>> Is there a way to set the size of std::vector <std::string> formulas to
>>> max_ncp size ?
>>>
>>> Something like "std::vector <std::string> formulas [max_ncp];"
>> When that max_ncp is compile-time known immutable value then
>> std::array<std::string, max_ncp> can be what you want.
>> Maybe worth to note that I've seen reserve(n) of std::vector
>> overused
>> in practice as bad pessimization. Vector is typically designed so that
>> we get log(max) allocations and max times element copies because
>> of vector just growing freely during its life-time. That can be turned into
>> way worse by someone micromanaging it.
>
> Now I am wondering if I should be using std::array instead of std::vector.

Only if the size of the vector will never change after it's created (I
don't think you mentioned that).  And in that case, you could use either
a std::array of std::string:

    std::array<std::string, max_ncp> formulas;

or a plain array of std::string:

    std::vector formulas[max_ncp];

Both require max_ncp to be a constant expression.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */