CODEWITHSUNDEEP
c++new-operator
karthik
karthik

Reputation: 17842

How to delete the object that is create inside the local function in c++?

I will explain the scenario using example.

   void func()
   {
          CLine* pObj = new CLine();
   }
   void func2()
   {
   }

How to delete the CLine object in func2()? Is it possible?

Thanks

Upvotes: 3

Views: 1629

Answers (6)

cppcoder
cppcoder

Reputation: 23115

You have to delete the object you created dynamically in a function inside the function itself. If you leave the function without deleting it, you cannot delete it and the memory is lost.

Upvotes: 0

Mankarse
Mankarse

Reputation: 40613

There is probably no need to use a free-store allocated variable at all in this case. Just do:

void func()
{
       CLine obj;
}
void func2()
{
}

obj will be automatically destroyed at the end of the scope.

If the variable absolutely must be free-store allocated, then you can put it in an unique_ptr as follows:

void func()
{
       const std::unique_ptr<CLine> obj(new CLine());
}
void func2()
{
}

if you are using c++03 then just replace unique_ptr with auto_ptr.

Anyway, if you really must use the code exactly as it is in your example then there is a way to still delete the CLine object. You have to use overloaded operator new and operator delete. It would have to be something like:

#include <vector>
#include <new>
#include <algorithm>
struct CLine {
    //... Other members ...

    static std::vector<void*> pointerCache;

    void* operator new(std::size_t size) throw(std::bad_alloc) {
        while (true) {
            void* pointer(malloc(size));
            if (pointer) {
                try {
                    pointerCache.push_back(pointer);
                    return pointer;
                }
                catch (std::bad_alloc&) {
                    free(pointer);
                }
            }
            if (std::new_handler handler = std::set_new_handler(0)) {
                std::set_new_handler(handler);
                (*handler)();
            }
            else {
                throw std::bad_alloc();
            }
        }
    }

    void operator delete(void *p) throw() {
        pointerCache.erase(std::remove(pointerCache.begin(), pointerCache.end(), p),pointerCache.end());
        free(p);
    }

    void* operator new(std::size_t size, std::nothrow_t const&) throw() {
        try {
            return operator new(size);
        } catch (std::bad_alloc&) {
            return 0;
        }
    }
    //Compressed for space constraints.
    void operator delete(void *p, std::nothrow_t const&) throw(){
        operator delete(p);}
    void* operator new[](std::size_t size) throw(std::bad_alloc){
        return operator new(size);}
    void operator delete[](void *p) throw(){operator delete(p);}
    void* operator new[](std::size_t size, std::nothrow_t const& nothrow) throw(){
        return operator new(size, nothrow);}
    void operator delete[](void *p, std::nothrow_t const& nothrow) throw(){
        operator delete(p, nothrow);}
};
std::vector<void*> CLine::pointerCache;

And then your code could look like this:

void func()
{
    CLine* pObj = new CLine();
}
void func2()
{
    //The most recently added pointer in CLine::pointerCache is
    // the one that was added in func()
    delete static_cast<CLine*> (CLine::pointerCache.back());
}

int main()
{
    func();
    func2();
}

But really, there is so much wrong with this code that you would be better just changing your design. Some of the problems include: the total confusion that you will cause to people reading your code, the lack of thread-safety, and the use of a global pointerCache object.

Upvotes: 3

Searock
Searock

Reputation: 6478

Yes you can.

void func()
{
     CLine* pObj = new CLine();
}

void func2(CLine* pObj)
{
     delete pObj;
}

if you pass CLine pointer to func2

Upvotes: 1

user236520
user236520

Reputation:

It IS possible if func() and func2() are methods of the same class, and pObj is a member variable of that class. I realize this is not how you structured your question, but this is one way to get the effect you are looking for

class MyClass
{
    CLine* pObj;

     void func()
     {
          pObj = new CLine();
     }
     void func2()
     {
         delete pObj;
     }
}

Upvotes: 1

Adam Maras
Adam Maras

Reputation: 26863

No, it's not possible. Because the only copy of the pointer is lost when func goes out of scope, you no longer have a reference to the memory to use with operator delete.

Upvotes: 0

Mark B
Mark B

Reputation: 96251

It's not possible. As soon as func finishes you've lost all reference to pObj and leaked its memory.

Upvotes: 13

Related Questions