Re: [Newbie][Intrusive] - Beginners question

From: i.nixman_at_[hidden]
Date: 2020-10-21 14:54:56

On 2020-10-21 14:33, Gaier, Bjoern via Boost-users wrote:
> Hey everybody,
> 
> I looked into the boost intrusive container and played around with it
> a bit. I tried the following code:
> struct animal : public boost::intrusive::list_base_hook<>
> {
>                 std::string name;
>                 int legs;
> 
>                 animal(std::string n, int l) : name{std::move(n)}, 
> legs{l} {}
> };
> 
> int main(int argc, char **argv)
> {
>                 std::vector<animal>            test;
>                 boost::intrusive::list<animal> wuff;
> 
>                 for(int n = 0; n < 5; n++)
>                 {
>                                test.push_back(animal("Katze", 4));
>                 }
> 
>                 for(int n = 0; n < 5; n++)
>                 {
>                                wuff.push_back(test[n]);
>                 }
> 

because `test` has 5 elems:

>                 for(int n = 0; n < 15; n++) 
> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>                 {
>                                wuff.push_back(test[n]);
>                 }

> 
>                 for(auto elem : wuff)
>                 {
>                                printf("%s\n", elem.name.c_str());
>                 }
> }
> 
> This code does crash! I guess this is because "test" relocated the
> memory and therefor "wuff" lost its references. I would expect the
> same result if I would have a std::list with pointers to animal
> structures - this is why I wonder what the benefit of an intrusive
> container is compared to the same container with just pointers in it.
> 
> Hope someone can explain me this! Thank you in advance and kind 
> greetings
> Björn
> Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816,
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> 
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