std::vector doesnt accept my struct as template

» cpp » std::vector doesnt accept my struct as template

By : user2186271

Date : November 24 2020, 04:01 AM

With these it helps Formally speaking, tabs needs to be a complete type when std::vector sees it. So even a forward declaration of tabs (which would denote an incomplete type) is not sufficient.
That means that the struct definition has to appear before CMenu.

code :

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Aligning template vector struct for SSE

By : Brandon

Date : March 29 2020, 07:55 AM

like below fixes the issue I am writing a software rasteriser using MSVC++ Express 2010 for windows. I am using SSE and need aligned data structures. I have a number of separate vector structs for different fundamental data types (float, int etc.) that I want to roll into one templated struct for convenience. The _declspec(align(16)) tag which has served well for aligning structs doesn't appear to work for templates. What are my options? This is what I would like to achieve: , The declspec is in the wrong place. It should be after the struct.

code :

template<typename T> 
struct _declspec(align(16)) baseVector 
{
    T v[4];
};

vector of template struct

By : MaWei

Date : March 29 2020, 07:55 AM

To fix the issue you can do As the error says, variables (including data members) can't be templates; only classes and functions can be.
It looks like you want the table to be able to hold values of various different types, specified at run-time according to which types are passed to add(). For that, you need dynamic types, which aren't directly supported in C++. You might consider libraries like Boost.Any or Boost.Variant for that.

code :

template <typename T>
class ValTable {
public:
    ValTable();
    void add(string,T);
    const bool find(string);
    void remove(string);
private:
    std::vector<ValNode<T>*> vals;
};

C++ struct with template in vector

By : Duygu Altinok

Date : March 29 2020, 07:55 AM

like below fixes the issue All your different Object classes are different types with different sizes. You can't put them in a homogenous container.
You would need some base class or base interface, and store pointers in the vector, relying on virtual dispatch and polymorphism when you pull the elements out. This would make your container of Objects a heterogenous container.

code :

struct Object
{
    set<string> names;
    string description;
};

vector<Object> easy;

multi inheriting a struct from struct and template struct, ordering matters when accessing base non-template struct data

By : user2160133

Date : March 29 2020, 07:55 AM

wish of those help , Hm, I think I see where the problem lies:

code :

struct D : B<D>, A { };

struct D
{
    B<D> implicitly_inherited_B_D;
    A    implicitly_inherited_A;
};

D* d    = new D();
void* v = d;
A* a    = static_cast<A*>(v);

D* d    = new D();
void* v = &d->implicitly_inherited_B_D;
A* a    = static_cast<A*>(v);
// or equivalent:
A* aa   = reinterpret_cast<A*>(&d->implicitly_inherited_B_D);

D* d    = new D();
void* v = static_cast<A*>(d);
// now this will work fine (v points to D's A part):
A* a    = static_cast<A*>(v);
D* dd   = static_cast<D*>(a); // even this one, original object was constructed as D

D* d  = new D();
A* a  = d;
D* ds = static_cast<D*>(a);
D* dr = reinterpret_cast<D*>(a); // actually undefined behaviour!!!

std::cout << d << std::endl << a << std::endl << ds << std::endl << dr << std::endl;

void* v = d; // -> need to go back via static_cast<D*>!

A* a    = static_cast<A*>(v);    // requires v = static_cast<A*>(d);
B<D>* d = static_cast<B<D>*>(v); // requires v = static_cast<B<D>*>(d);