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non standard extension warning when searching in a vector of unique_ptrs


non standard extension warning when searching in a vector of unique_ptrs

By : Paris Duane
Date : November 22 2020, 02:59 PM
this will help find_if returns the iterator to the matching element by value, and you're trying to bind that to a non-const reference, which is illegal. The VC++ compiler has an infamous extension that allows this, but thankfully generates a warning when you set /W4. Change your code to
code :
auto itr = std::find_if(...);


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Moving unique_ptrs from one vector to another

Moving unique_ptrs from one vector to another


By : user3001072
Date : March 29 2020, 07:55 AM
may help you . Your code looks basically correct to me, except that it seems like you intend for the moved-from unique_ptr to be erased from the unsorted vector:
code :
std::vector<std::unique_ptr<T> > unsorted, sorted;
// fill the "unsorted" vector
while( unsorted.size() > 0 )
{
    const auto it = find_next_element_to_add_to_sorted(unsorted);
    sorted.push_back( std::move(*it) );
    unsorted.erase(it);
}
Iterating through a unique_ptr of a vector of unique_ptrs

Iterating through a unique_ptr of a vector of unique_ptrs


By : cola han
Date : March 29 2020, 07:55 AM
I wish this help you You can't copy unique pointers because... well, they are unique.
You should iterate by reference:
code :
for (auto & item : *v)
//       ^^^
Transferring Ownership in vector of unique_ptrs

Transferring Ownership in vector of unique_ptrs


By : Rahul Gunjal
Date : March 29 2020, 07:55 AM
it fixes the issue I have 2 classes A and B , This code runs fine on both gcc 4.9.2 and Visual Studio 2013:
code :
#include <iostream>
#include <memory>
#include <vector>
#include <algorithm>

using namespace std;

//A.h
class A{
public:
    int alpha;
    A(int input) : alpha(input){}
};

// B.h
typedef unique_ptr<A> APtr;
typedef vector<APtr> BVEC;

class B
{
public:
    BVEC vec;
    B(){}
    const B& operator=(const B& b){
        vec.clear();
        for_each(b.vec.cbegin(), b.vec.cend(), [&](const unique_ptr<A>& i){vec.push_back(unique_ptr<A>(new A(*i))); });
        return b;
    }
    B(const B& b){
        vec.clear();
        for_each(b.vec.cbegin(), b.vec.cend(), [&](const unique_ptr<A>& i){vec.push_back(unique_ptr<A>(new A(*i))); });
    }
    const B& operator=(B&& b){
        vec.resize(b.vec.size());
        move(b.vec.begin(), b.vec.end(), vec.begin());
        return *this;
    }
    B(B&& b){
        vec.resize(b.vec.size());
        move(b.vec.begin(), b.vec.end(), vec.begin());
    }
};

int main() {
    B foo;
    B bar;

    for (auto i = 0; i < 10; ++i){
        foo.vec.push_back(unique_ptr<A>(new A(i)));
    }
    bar = foo;
    foo.vec.clear();

    for (auto& i : bar.vec){
        cout << i->alpha << endl;
    }
    foo = move(bar);

    for (auto& i : foo.vec){
        cout << i->alpha << endl;
    }
    return 0;
}
Copying a vector of structs containing unique_ptrs

Copying a vector of structs containing unique_ptrs


By : wubin
Date : March 29 2020, 07:55 AM
Any of those help The first thing to understand is you can only have one std::unique_ptr object containing a pointer to a particular object. Your Skin(const Skin& s) constructor violates this principle, resulting in two copies of a unique_ptr. If you have an object containing unique_ptr members, you'll need to do one of the following:
Not have a copy constructor or assignment operator. In the copy constructor and/or assignment operator, allocate a new copy of the underlying resource. This would require calling al_clone_bitmap to duplicate the resource.
code :
std::unique_ptr<ALLEGRO_BITMAP> black(al_create_bitmap(groundWidth, TILESIZE));
Skin::Skin(std::unique_ptr<ALLEGRO_BITMAP>&& bitmap)
    : img(bitmap)
{
}
Skin(std::move(black))
Skin::Skin(const Skin& s)
    : img(al_clone_bitmap(s.img.get()))
{
}
How to insert several unique_ptrs into vector at once

How to insert several unique_ptrs into vector at once


By : 양지윤
Date : March 29 2020, 07:55 AM
This might help you There is two different kinds of memory being allocated here. There is the memory allocated in the vector for the unique_ptr itself (which will not be very much, just a pointer per unique_ptr). And then the dynamically allocated memory for the object managed by each unique_ptr.
You cannot allocate all the memory up-front as the dynamically allocated memory for the object within each unique_ptr must be allocated separately.
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