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Following program looks pretty OK to me. But I can not get it compiled.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
struct a
{
int i;
int j;
};
std::vector<a*> vecA;
a* pA = new a;
pA->i = 4;
pA->j = 9;
vecA.push_back(pA);
return 0;
}
It generates following error.
struct_update.cc: In function ‘int main()’:
struct_update.cc:32:19: error: template argument for ‘template<class _Alloc> class std::allocator’ uses local type ‘main()::a*’
struct_update.cc:32:19: error: trying to instantiate ‘template<class _Alloc> class std::allocator’
struct_update.cc:32:19: error: template argument 2 is invalid
struct_update.cc:32:25: error: invalid type in declaration before ‘;’ token
struct_update.cc:39:10: error: request for member ‘push_back’ in ‘vecA’, which is of non-class type ‘int’
832
You can store pointers in a vector just like you would anything else. Declare a vector of pointers like this: vector<MyClass*> vec; The important thing to remember is that a vector stores values without regard for what those values represent.
You can actually create a vector of structs!
To assign a pointer to 'point to' an instance of an object use pointer = &vector_of_reviews . The & operator gets the address of something, and it's this that you want to assign to the pointer. *pointer = vector_of_reviews dereferences the pointer (obtains the actual object 'pointed to').
Having vector of objects is much slower than a vector of pointers. The results are because algorithms such as sorting need to move elements inside the container. So they not only read the data but also perform a copy (when the algorithm decides to swap items or move to a correct place according to the order).
This isn't true anymore in the new C++11 standard, but current compilers don't fully implement it yet.
A local type can't be a template parameter. Move your structure definition above main, and everything will work.
Or update your compiler to one that supports this part of C++11.
Here's the restriction from C++03 section 14.3.1 ([temp.arg.type]), which is removed in C++11:
A local type, a type with no linkage, an unnamed type or a type compounded from any of these types shall not be used as a template-argument for a template type-parameter.
92
Move the structure definition out of main function.
struct a
{
int i;
int j;
};
int main()
{
std::vector<a*> vecA;
a* pA = new a;
pA->i = 4;
pA->j = 9;
vecA.push_back(pA);
In C++03 you cannot do this
A local type, a type with no linkage, an unnamed type or a type compounded from any of these types shall not be used as a template-argument for a template type-parameter.
In C++11 i think you can according to the standard. Even though my Visual Studio 11 compiler refuses to allow it
30
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