Problem passing double array as a function parameter

Hi,

I'm using Visual C++. Let say I want to pass a const NxN matrix to a function, what syntax structure would allow the function to accept multiple value of N?

Currently, if I want to pass a 3x3 matrix, my function parameter would look like

void fn(int matrix[][3], int length)

Without [3], the code won't compile. I want the function to be able to take on a 5x5 matrix as well. I tried to use pointer like int ** matrix. But then when I access the matrix, the compiler complains about not knowing its dimension...

please help.


thank you

From what I see, the compiler needs to know the size of the inner array.

One solution could be to use a function template:

Code:

---

template <typename T>
void fn(T matrix, std::size_t size_x, std::size_t size_y)
{
}

---

Still, have you considered using/writing a matrix class that suits your needs?

hi if you know pointers then mayb this can help.
create one pointer that points to a dynamic array with base type that is a POINTER TYPE.then each row of yor matrix can b represented by the corresponding pointer in this dynamic array. (so if you want 5 rows then u should hav the pointers p1, p2, p3, p4, p5 in this dynamic array)create dynamic arrays with base type int, double or whatever, for each of these pointers and fill them up with the correspondin elements in your matrix.

finally,when u call your fnuction mak your function take in as argument that pointer with the pointer base type u created earlier. this pointer is basically your nxn matrix

so your function declaration would look somethin like :
returntype function(pointerOfArrayOfPointers *p);
but make sure u define the type pointerOfArrayOfPointers with: typedef int* pointerOfArrayOfPointers somewhere outside of main

Quote:

---

Originally Posted by laserlight

From what I see, the compiler needs to know the size of the inner array.

One solution could be to use a function template:

Code:

---

template <typename T>
void fn(T matrix, std::size_t size_x, std::size_t size_y)
{
}

---

Still, have you considered using/writing a matrix class that suits your needs?

---

Thanks for the suggestion. Both methods would work, but I don't think they are allow in my assignment. The assignment focus is not on C++ language anyways. I'm just trying to find ways to shorten my code (without overdoing it).

Quote:

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Originally Posted by henrychan22

so your function declaration would look somethin like :
returntype function(pointerOfArrayOfPointers *p);
but make sure u define the type pointerOfArrayOfPointers with: typedef int* pointerOfArrayOfPointers somewhere outside of main

---

Hi,

I just gave it a shot and it seems to work pretty well. Thanks

The only problem seems to be that I can no longer define a double array like

Code:

---

int m[][2] = { { 1, 1 }, {1, 1} }

---

Instead, I have to do it row by row, then put everything into the array pointer. A small price to pay I guess.

What you're basically talking about is this 'C' hack.
http://c-faq.com/aryptr/ary2dfunc2.html

You should really have a better (ie safer) way of solving the problem in C++.
Templates are one way, vectors are another.

If someone is teaching you this in a C++ course, they're not doing a good job IMO.

Quote:

---

Originally Posted by Salem

What you're basically talking about is this 'C' hack.
http://c-faq.com/aryptr/ary2dfunc2.html

You should really have a better (ie safer) way of solving the problem in C++.
Templates are one way, vectors are another.

If someone is teaching you this in a C++ course, they're not doing a good job IMO.

---

I agree. I don't like to use hacks on code too. But I just want to use the simplest ways to solve this problem that I thought was trivial initially (the problem won't occur at all in Java)

Rest assure, it is not a C++ language course.