how can i test how many dimensions have the array?

[Cambalinho]

seen these array:
int data[4][5][5][6];
we know that array have 4 Dimensions...
can we calculate how many dimensions 1 array have it?

[jonnin]

you don't need to calculate it. Its right there. Why do you want to calculate what you already know at code-writing time? To me this is like

const int x = 1234;
//how can I compute the value of x?

I think std::array will provide this info. I don't know if you can back it out easily of an array or not.

[Cambalinho]

just playing with code... but think in these way: if i can calculate the number of array elements:

#include <iostream>
using namespace std;

template<class T>
int ArrayCountElements(T &a)
{
    return sizeof(a) / sizeof(a[0]);
}

int main()
{
    int data[4][5][5][6];
    int dataSize = ArrayCountElements(data[0]);
    cout << dataSize;
    return 0;
}

why not calculate the array dimensions!?!
i'm just playing with code and learn more

[jonnin]

return sizeof(a) / sizeof(a[0]);

this does not tell you the # of dimensions, it tells you the size of one of the dimensions.
are you asking how to know its 4d instead of 2d, or how big each piece is? The first, I do not see a way to get it. The second you can get as you show here, yes.

you are on the right track if you want to know the length of one dimension.

[coder777]

Maybe this is what you want:

http://www.cplusplus.com/reference/type_traits/rank/

[jonnin]

That would do it.
Do you know HOW it works to roll it yourself for educational purposes?! Or is it tapping something at compile time that we can't get at?

[Cambalinho]

if i use on code(for test):
data[0][0][0][0][0]=20;
i will get a compiler error, so i can't test the executed errors and see if is 2D or 3D array

[Cambalinho]

coder777: yes, but the rank use the type name, instead a var name

[jonnin]

try this for fun

#include <bits/stdc++.h>
#include <iostream>
using namespace std;
int main()
{
int data[4][5][5][6];
 decltype(data) x; 
cout << typeid(x).name()<<endl;
}

the i is int ... so it tells you # of dimensions and size of each one all in one statment, or you can parse it out cleaner if you dislike the format. A is array, I suppose. I didnt read the docs on it, just guessing. If you want the actual value 4, you have to parse the string a little. Counting the underscores may work, at least for basic types like int. I don't know what it will spew if you have a class.

all that to tell you back what you typed in :P

[Cambalinho]

thank you so much to all for all

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

template<class T>
int ArrayCountElements(T &a)
{
    return sizeof(a) / sizeof(a[0]);
}

template<class T>
int ArrayCountDimentions(T &a)
{
    decltype(&a) x; //must be the adress operator
    string data = typeid(x).name();
    int CountDimention=0;
    for(int i=0; i<data.size();i++)
    {
        if(data[i]=='A')//the 'A' is upper case and the int is 'i'
        {
            CountDimention++;
        }
    }
    return CountDimention;
}

int main()
{
    char data[4][5][5][6];
    cout << ArrayCountDimentions(data);
    return 0;
}

thank you

[jonnin]

right, mine worked because the name of an array can collapse to a pointer/address.
you now have 30 lines to figure out what line 29 said.
amusing exercise, at least. I had to look it up, so I learned something as well.

[Cambalinho]

creates a 4D array with random values :P

[JLBorges]

See: https://en.cppreference.com/w/cpp/types/rank#Possible_implementation

[Cambalinho]

using that way, i can test if the variable is an array:

template<class T>
bool IsAnArray(T &a)
{
    decltype(&a) x; //must be the adress operator
    string data = typeid(x).name();
    for(int i=0; i<data.size();i++)
    {
        if(data[i]=='A')//'A' is an array indication
        {
            return true;
        }
    }
    return false;
}

[George P]

If you need to know the number of elements in each dimension of the array it looks like std::extent would do it:

http://www.cplusplus.com/reference/type_traits/extent/

[Enoizat]

i can test if the variable is an array

Yet another link:
https://en.cppreference.com/w/cpp/types/is_array
:-)