How to put 2-dimensional Array's pointer to the function as the parameter

Question

I'm solving an algorithm problem using C++.

I want to put the pointer of 2-dimensional array that having different sizes of each dimension by init input dynamically.

What I coded as a function is below: the contents(the function of function) mean nothing.

int cal(int **arr){
int test = arr[0][0];
return 0;
}

And the result of this function

int arrayD[totalGroupCount][totalBeadCount];

int a = cal(arrayD);

It just says "No Matching function call for 'cal'"

I did declare the function 'cal'.

And I did it a lot with different symbol

int cal(int *arr[]){
int test = arr[0][0];
return 0;
}

But it says me identically.

I already searched for this question but answers I got make just the same error(I totally don't understand how they make it)

Note that type of `int arr[0][0]` is actually `int *` and not `int **`. — Dima Tisnek, Oct 12 '15 at 16:37
Please read up on multidimensional arrays, e.g. here: http://www.cplusplus.com/doc/tutorial/arrays/ — Dima Tisnek, Oct 12 '15 at 16:38
@qarma: Err, what? The type of `int arr[x][y]` is `int[x][y]` not `int*`. — alk, Oct 12 '15 at 16:41
@alk Thank you for your answer but totalBeadCount is dynamic integer value... — LKM, Oct 12 '15 at 16:47
Then pass is a first parameter to the function: `int cal(size_t totalBeadCount, (arrayD*) [totalBeadCount]);`. This however is very Cish, C++ provides much more elegant ways to solve this. — alk, Oct 12 '15 at 16:49
`a = cal(&arrayD[0])` should compile. But this is not recommended anyway. In practice, casting a multidiensinal array to a pointer works only if the dimensions of the array are known except the first one. Since you have C++, use it, use stl! — A.S.H, Oct 12 '15 at 16:49
@alk details, details, I'm saying what it's logically closer to — Dima Tisnek, Oct 12 '15 at 16:51

score 2 · Answer 1 · answered Oct 12 '15 at 16:49

As you use c++, there's better solution with std::vector< vector<int > >

int cal(std::vector<std::vector<int> > arr)
{
    int test = arr[0][0];
    return 0;
}

And call the function

std::vector<std::vector<int> >arrayD (totalGroupCount, std::vector<int>(totalBeadCount));
int a = cal(arrayD);

Also you can use push_back() function to dynamically add element to the vector.

ForceBru · Answer 2 · 2015-10-12T16:44:22.943

0

You need to allocate memory with malloc, calloc, or new:

long a;
int **pt; // a pointer to pointer to int
pt=new int*[rows]; // allocate memory for pointers,
// not for ints

for (a=0;a<rows;++a) pt[a]=new int[columns]; // here you're allocating
// memory for the actual data

This will create an array similar to pt[rows][columns].

Then you pass pt like this:

int Func(int **data) {
//do something
return //something
}

Func(pt);

edited Oct 12 '15 at 16:44

answered Oct 12 '15 at 16:38

ForceBru

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Is it the only answer? It's complicated and I don't understand why I should code like this way, not using basic way – LKM Oct 12 '15 at 16:40
@LKM, what way is _basic_? – ForceBru Oct 12 '15 at 16:41
@lkm It's not a basic way what you're doing, but actually a non standard c++ extension called variable length arrays. – πάντα ῥεῖ Oct 12 '15 at 16:42
2

Too many words. "Use `std::vector`" is all that's needed. – n. m. could be an AI Oct 12 '15 at 16:47
Why give a solution which ignores the prerequisite given by the OP, that is linear array, not a scattered one? – alk Oct 12 '15 at 16:48
@alk, the OP just wants a 2D array and doesn't care about its placement in memory, does he? – ForceBru Oct 12 '15 at 16:50
@n.m., you're right, but the OP clearly says he wants a 2D array, not a vector, so I had to work with arrays as well – ForceBru Oct 12 '15 at 16:52
2

No, OP very clearly says nothing about vectors. Normally people want to solve problems, not to use specific library facilities. – n. m. could be an AI Oct 12 '15 at 16:59
From the OP: `int arrayD[totalGroupCount][totalBeadCount]; ` – alk Oct 12 '15 at 17:10

How to put 2-dimensional Array's pointer to the function as the parameter

2 Answers2