Re: Reserve vector with 100 strings each of fixed size 20

From:
Diwa <shettydiwakar@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 15 Sep 2009 14:06:50 -0700 (PDT)
Message-ID:
<4af2e5df-9936-48a1-a8a1-6ec5dc62d1ce@f10g2000vbf.googlegroups.com>
On Aug 26, 5:55 pm, Juha Nieminen <nos...@thanks.invalid> wrote:

Diwa wrote:

I know I canreservespace for100stringsin avectorby doing
following:

std::vector<std::string> m_vec;
m_vec.reserve(100)

But I also know that each of the string will be exactly 20 chars.
Can I use this fact while reserving thevectorspace above?


  If you know that all thestringswill be exactly 20 chars, and
especially if you know that will not change, you can use a char array
instead. Of course arrays cannot be used directly with std::vector, but
they can if you enclose them in a struct, like this:

struct My20CharString
{
    char str[21];
    My20CharString(): str() {}

};

std::vector<My20CharString> m_vec;
m_vec.reserve(100);

  If you don't like having to write "m_vec[i].str" instead of just
"m_vec[i]", then you could do this:

struct My20CharString
{
    char str[21];

    My20CharString(): str() {}
    operator const char*() const { return str; }
    operator char*() { return str; }

};- Hide quoted text -

- Show quoted text -


Thanks Juha. Seems like I will go this route of a struct containing
char[21] because we want to persist info to disk

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