Challenge: write a function that returns a matrix of function pointers

Question

Weird challenge :)
Look my solution: https://code.sololearn.com/cfxZARGS1AR3/#cpp

Answer 1

@Andrea

What is a matrix?

This right? - int matrix[3][3];
This one is the same as int ** matrix, as an array is nothing but a pointer. And a pointer to a pointer == 2D Array...

Or this? - https://code.sololearn.com/cq24J951TxgI/?ref=app

BTW how will you assign functions to the matrix of functions?
As input won't work...
So you'll have to do it manually...

Here is something I can think of. Please guide me...

typedef int(*fx)(int,int)** FxMatrix;
typedef int(*fx)(int,int) FxType;

FxMatrix Assign( int(*fx1)(int,int), int(*fx2)(int,int), int(*fx3)(int,int), int(*fx4)(int,int))
{
FxMatrix mat={{fx1, fx2},
{fx3, fx4}};
return mat;
}
int add(int a, int b)
{ return a+b; }
int sub(int a, int b)
{ return a-b; }
int mul(int a, int b)
{ return a*b; }
int div(int a, int b)
{ return a/b; }

int main()
{
FxMatrix matrix = new FxType*[2];
for(int i=0;i<2;i++) matrix[i] = new FxType[2];
matrix = Assign( &add, &sub, &mul, &div );
for(int i=0;i<2;i++)
for(int j=0;j<2;j++)
cout<<matrix[i][j](2,2);

//Prints 4,0,4,1...
}

Answer 2

@kinshuk i dont know with your method. I dont use vector, instead i use dear old malloc()

Answer 3

@kinshuk
you said too much time pointers 😂😂😂
but no...surely not like this
remember that matrix are not pointer to pointers and rembember that someone invented typedef word

Answer 4

@kinshuk

I think your class is great but now i can't control 2300 lines.
You make a mistake: array are not pointers and matrix are not pointers to pointers. What? http://c-faq.com/aryptr/aryptrequiv.html

"A reference to an object of type array-of-T which appears in an expression decays (with three exceptions) into a pointer to its first element; the type of the resultant pointer is pointer-to-T."

Now if an array decays in a pointer....a matrix?
Try yourself:
int matrix[10][20];
int **P = matrix; // Error: cannot convert a int(*)[20] into a (int**)
int (*p)[20] = matrix; //Ok
What does it mean? It's difficult to explain for me in english but matrix is an pointer-to-matrix that automaticaly decays into a pointer-to-array of 20 elements.
So matrix points first 20 elements.

When you create a matrix using pointers-to-pointers you have to do something that using pointers-to-array you have not to do: create an array of pointers.

Because the pointers-to-array has an information that the pointer-to-pointer has not: number 20.

Look my code and how its simple create a matrix using only one pointer-to-array. There is a little example. Then i will post another code for explain my solution for this challenge.

However your little code is not so bad, but you create it in the main: I want a function that create and return a matrix to the main ;)

P.S. typedef int(*fx)(int,int)** FxMatrix; is not ok for the compiler :P

Answer 5

@kinshuk

Yes automatically an array decays into a pointer to its first element, specially when it is an argument of a function ;)
If you want, look my solution here: https://code.sololearn.com/cfxZARGS1AR3/#cpp

Answer 6

Though I didn't win this challenge, I learned many new things.
Thank You very much!

https://code.sololearn.com/c10itmF1cL6V/?ref=app

Answer 7

Thanks for playing!!!

Answer 8

@Andrea
Waiting for the next challenge.
I will try to win that one!

Answer 9

New challenge is coming 😂

Answer 10

New challenge is ready 😃
https://www.sololearn.com/Discuss/468186/?ref=app

Answer 11

Yes it is 😄

Answer 12

a matrix of function pointers?

Something like this?

vector<vector<int(*func)(int,int)>> ?

How will one assign functions to this?

Answer 13

I have no idea how you declare a pointer of pointers to a pointer to a function.

Like this maybe?

int (*func)(int,int) ** function_array;

Answer 14

@Andrea
Yeah since the typedef if not working, I converted it to a define, and that works...

I had read that a function which has an array as an argument:

int func(int arr[10])

reads it like this:

int func(int *arr)

Maybe Im confused. Ill have to study the tutorials again...

Answer 15

@Andrea
Im returning the matrix in main.
How can you simply print a matrix of function pointers without saving it in another variable of the same type, after all its a matrix!
You want me to use print function?
How will that return a matrix?

I can think of this:

void print(FxMatrix a);

In main:

print(assign(...));
//Returns a rvalue ref which is used by print...

Answer 16

@Andrea
Youre doing the same thing -_-
Returning a matrix in main to a matrix variable...

Answer 17

Sounds interesting...