Function parameter: Pointer to array of objects

Question

In my main function I create an array of objects of a certain class "Menu"

And when I call a function I want to provide a pointer to that array.

Menu menu[2];
// Create menu [0], [1]
Function(POINTER_TO_ARRAY);

Question: What is the correct way to write the Function parameters?

I try:

Function(&menu);

and in Header file:

void Function(Menu *menu[]); // not working
error: Cannot convert parameter 1 from Menu(*)[2] to Menu *[]

void Function(Menu * menu); // not working
error: Cannot convert parameter 1 from Menu(*)[2] to Menu *[]

and I can't come up with any other way to do this and I can't find a solution to this particular problem.

Simply, I want to be able to access the Menu array within the function through a pointer. What are the difference in normal pointer to a pointer to an array?

hmjd · Accepted Answer · 2012-08-08 14:16:41Z

10

Declaration:

void Function(Menu* a_menus); // Arrays decay to pointers.

Invocation:

Function(menu);

However, you would need to inform Function() how many entries are in the array. As this is C++ suggest using std::array or std::vector which have knowledge of their size, beginning and end:

std::vector<Menu> menus;
menus.push_back(Menu("1"));
menus.push_back(Menu("2"));

Function(menus);

void Function(const std::vector<Menu>& a_menus)
{
    std::for_each(a_menus.begin(),
                  a_menus.end(),
                  [](const Menu& a_menu)
                  {
                      // Use a_menu
                  });
}

edited Aug 8, 2012 at 14:16

answered Aug 8, 2012 at 14:09

hmjd

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Comments

TemplateRex · Accepted Answer · 2012-08-08 14:21:37Z

3

Either by const or non-const pointer

void Function(Menu const* menu);
void Function(Menu* menu);

...or by const or non-const reference

void Function(Menu const (&menu)[2]);
void Function(Menu (&menu)[2]);

which can be generalized to a template so that the array size will be deduced by the compiler:

template<size_t N> void Function(Menu const (&menu)[N]);
template<size_t N> void Function(Menu (&menu)[N]);

Always call as Function(menu);

edited Aug 8, 2012 at 14:21

answered Aug 8, 2012 at 14:09

TemplateRex

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Comments

mathematician1975 · Accepted Answer · 2012-08-08 14:33:57Z

3

Should work if you use

 void Function(Menu * menu);

and call using

Function(menu);

instead of

Function(&menu);

passing the array name causes it to decay to a pointer to the type contained in the array. However, as @hmjd says in his answer you will also need to pass the array size, so his suggestion of using a vector is favourable if this option is open to you.

edited Aug 8, 2012 at 14:33

answered Aug 8, 2012 at 14:11

mathematician1975

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Comments

huseyin tugrul buyukisik · Accepted Answer · 2012-08-08 14:18:03Z

0

You can use

Function((void *) whatever_pointer_type_or_array_of_classes);

in your main.

And in the function:

type Function(void * whatever)
{
    your_type * x =(your_type *) whatever;
    //use x 
    ....
    x->file_open=true;
    ....
}

answered Aug 8, 2012 at 14:18

huseyin tugrul buyukisik

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