Why's wrong with this template? how can I compile it correctly

Question

#include "test.h"
template<typename T>
test<T>::test(const T &elem):data(elem)
{
}

template<typename T>
test<T>::~test()
{
    delete data;
}
template<typename T>
class test
{
private:
    T data;
public:
    test(const T &elem);
    ~test();
};
#include"test.h"
int main()
{
    test<int> a(2);
}

Classes and implementations and main functions are written in different files by me, when i try to compile it ,The compiler will report an error,but i can't find what's wrong.

I have written the definition and implementation of the template in separate files and imported definition with a header file — chris_piglet, Dec 11 '19 at 15:52
"_The compiler will report an error,but i can't find what's wrong._" Hint: when asking about compiler errors, consider providing said compiler errors in the question. — Algirdas Preidžius, Dec 11 '19 at 16:04

score 2 · Answer 1 · answered Dec 11 '19 at 15:48

2

Your destructor as written:

template<typename T>
test<T>::~test()
{
    delete data;
}

assumes that data is a pointer. As it is declared having type T this means you cannot instantiate it with type int probably int * is the closest, but then your constructor does not make much sense. You probably want to remove delete statement from destructor, but it is difficult to say without seeing the whole picture.

answered Dec 11 '19 at 15:48

Slava

43,454
1
47
90

although I delate my destructor,the compiler also says errors like:LNK2019 and LNK1120. What dose that mean? – chris_piglet Dec 11 '19 at 16:15
@chris_piglet That mean error codes, but I am not a robot I read error messages in plain language – Slava Dec 11 '19 at 16:17
Do I have any other errors besides the constructor? – chris_piglet Dec 11 '19 at 16:22
@chris_piglet Yes — read the duplicate question that is linked in the big, blue post notice above. – Konrad Rudolph Dec 11 '19 at 16:25
thanks, my friends. Learning c++ is a real challenge – chris_piglet Dec 11 '19 at 16:32

score 0 · Answer 2 · answered Dec 11 '19 at 15:56

0

If you wish to use the delete call in your destructor, your class member should almost always be type T*. However, having a member of type T is based on your use-case, and if you do, that member has memory allocated based on how you instantiate your class (calling new() and having it on the heap, or on the stack as you have). In this scenario, deleting the member T also happens when you call delete() on your instantiated class object, or is removed automatically from the stack when your object goes out of scope.

answered Dec 11 '19 at 15:56

Uninitialized

151
5

OK you gotta tell me how you managed to post an answer to a closed question. – Konrad Rudolph Dec 11 '19 at 16:24
That's my superpower :P – Uninitialized Dec 11 '19 at 16:30

Why's wrong with this template? how can I compile it correctly

2 Answers2