template <class T> //do I need to define T somewhere?
class ResourceManager
{
private:
vector<T*> *items;
public:
void init()
{
items = new vector<T*>;
for (vector<T*>::iterator i = items->begin(); i != items->end(); i++) //<-- This is not accepted, "Expected ; before i"
{
//... do stuff
}
}
}
std::vector and template problem...
Author
Hi, I'm curious why the following doesn't work.
To me it should work, but this is my first attempt using templates, so I might be missing something. I also have the same problem with std::map.
Thanks for your time!
/Robert
You should be more specific than just saying "it doesnt work"... [EDIT] - ahh, I see you described the error in your comments, never mind!
Anyway, you need a semicolon on the end of your class definition, and you need "std::" in front of "vector". This works for me:
[EDIT]
As for style:
1) Dont use init functions! Use constructors and destructors:
2) Is there any reason that items is a pointer?:
Anyway, you need a semicolon on the end of your class definition, and you need "std::" in front of "vector". This works for me:
template <class T>class ResourceManager{ private: std::vector<T*> *items; public: void init() { items = new std::vector<T*>; for (std::vector<T*>::iterator i = items->begin(); i != items->end(); i++) { //... do stuff } }};[EDIT]
As for style:
1) Dont use init functions! Use constructors and destructors:
template <class T>class ResourceManager{private: std::vector<T*> *items;public: ResourceManager() { items = new std::vector<T*>; for (std::vector<T*>::iterator i = items->begin(); i != items->end(); i++) { //... do stuff } } ~ResourceManager() { delete items; }};2) Is there any reason that items is a pointer?:
template <class T>class ResourceManager{private: std::vector<T*> items;public: ResourceManager() { for (std::vector<T*>::iterator i = items.begin(); i != items.end(); i++) { //... do stuff } }};
The compiler is not certain that std::vector<T*>::iterator is actually referring to a type in this case — as far as it's concerned, it has as much chance of being a type as it does a member.
Just give it a hint that it's a type:
for ( typename std::vector< T* >::iterator i = ... )
Just give it a hint that it's a type:
for ( typename std::vector< T* >::iterator i = ... )
Quote:Original post by SiCrane
You're probably missing a typename keywordtypename vector<T*>::iterator
Serves me right for wandering away before posting.
Author
Hi!
"typename vector<T*>::iterator" did the trick!
I just noticed that I've left out quite a bit of information, for instance:
In my code I do have a semicolon after the class declaration, and "using namespace std". I also create and delete "items" in the constructor/destructor.
I guess I shouldn't post before going to sleep! :)
Also, about "items" being a pointer - I've read somewhere that the memory used when dynamically allocating variables is faster than putting it on the stack, so that's why. :)
Much appreciated, thanks again!
/Robert
"typename vector<T*>::iterator" did the trick!
I just noticed that I've left out quite a bit of information, for instance:
In my code I do have a semicolon after the class declaration, and "using namespace std". I also create and delete "items" in the constructor/destructor.
I guess I shouldn't post before going to sleep! :)
Also, about "items" being a pointer - I've read somewhere that the memory used when dynamically allocating variables is faster than putting it on the stack, so that's why. :)
Much appreciated, thanks again!
/Robert
Quote:Original post by Rasmadrak
Also, about "items" being a pointer - I've read somewhere that the memory used when dynamically allocating variables is faster than putting it on the stack, so that's why. :)
It's the contrary : putting/removing variables on the stack is faster that allocating/deallocating memory for them on the heap, unless you've written a damned good allocator for your types.
Quote:Original post by rolkAQuote:Original post by Rasmadrak
Also, about "items" being a pointer - I've read somewhere that the memory used when dynamically allocating variables is faster than putting it on the stack, so that's why. :)
And, regardless, std::vector stores elements dynamically, anyway, so why not just let it serve the purpose it's meant to (i.e. be a resizeable array that looks after its own memory) rather than abusing it?
Quote:Original post by TheUnbelieverQuote:Original post by rolkAQuote:Original post by Rasmadrak
Also, about "items" being a pointer - I've read somewhere that the memory used when dynamically allocating variables is faster than putting it on the stack, so that's why. :)
And, regardless, std::vector stores elements dynamically, anyway, so why not just let it serve the purpose it's meant to (i.e. be a resizeable array that looks after its own memory) rather than abusing it?
And, regardless that, the std::vector object will not necessarily be on the stack — it will be in the same storage as the enclosing ResourceManager-type object (i.e., if you do new ResourceManager then the vector will be allocated in the free store even without newing it manually).
Furthermore, and most importantly — you wouldn’t notice the difference anyway. Unless your algorithm were terribly wrong — in which case your performance bottleneck would be the algorithm and not your allocation method. So, to reiterate the Golden Rule — do not optimise prematurely.
Quote:Original post by SiCrane
You're probably missing a typename keywordtypename vector<T*>::iterator
Could someone explain why this needs to be typename'd? I'm not completely familiar with typenames, and I would have written this same for loop (without a typename) and would have had the same problem. Why doesn't that work just as an iterator for the for loop?
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