Pointer to Pointer...

[-dcx-]

I'm still new to programming and right now I'm having a little trouble understanding how pointer to pointer works. Can someone give me an explanation (a sample code would be great too).

[IfYouSaySo]

A pointer to a pointer is usually used when you want to update the address of a pointer. Why would you want to do this, you may ask? Well, sometimes you want the user of a function to provide you with a pointer to some data type, and you will return via that pointer malloc'ed memory to something. To be honest, I'm not sure how necessary this is in C++...usually you see this sort of thing in c code.

But...here's an example, which assumes the existence of some type SomeDataType, with a member function DoSomething. But hopefully you get the idea:

int main()
{
    SomeDataType* pSomeData = NULL;

    SomeDataTypeAllocator(&pSomeData);

    // we should have a valid pointer now
    if (pSomeData)
        pSomeData->DoSomething();

    SomeDataTypeFree(pSomeData);

    return 0;
}

void SomeDataTypeAllocator(SomeDataType** pData)
{
    if ( pData )
        *pData = new SomeDataType();
}

void SomeDataTypeFree(SomeDataType* pData)
{
    if ( pData )
        delete pData;
}

[master5001]

I tend to agree with IfYouSaySo. In C++ you would usually use references to pointers instead of pointers to them.

void some_func(int *&someptr) {
    someptr = new int;
}