Passing a multidimensional vector (matrix) to a Function in C++

Question

I am having problems passing a multidimensonal array to a function from main. Here is an example of the problem:

double function(int**);
int main(){
    vector< vector<int> > my_vec;
    double result;
    result = funtion(my_vec); //it doesnt recognize the type. my vec
    return 0;
}
double function(int**my_vec){
    // DOES STUFF WITH THE DATA
}

What is the correct way of passing the matrix to the function?

Redeclaring the function to take the correct type by-reference springs to mind. those two types (`int**` and `std::vector>` are quite-literally *worlds* apart. — WhozCraig, Feb 03 '15 at 20:04
You are definitely right !! now that I know the answer I dont know why I was trying int** !! — Duccio Piovani, Feb 03 '15 at 20:59
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score 4 · Accepted Answer · answered Feb 03 '15 at 20:02

4

What is the correct way of passing the matrix to the function ??

Change the signature of function to:

double function(vector< vector<int> >& my_vec);

answered Feb 03 '15 at 20:02

R Sahu

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score 2 · Answer 2 · answered Feb 03 '15 at 20:03

2

The correct way to accept the argument is:

double function(vector<vector<int>> const &);

unless the function needs to modify the argument, in which case use:

double function(vector<vector<int>> &);

The int** type signature is for raw C-style arrays: there's no reason to discard the helpful C++ container here.

answered Feb 03 '15 at 20:03

Useless

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Ok yes this make totally sense. – Duccio Piovani Feb 03 '15 at 20:58

score 0 · Answer 3 · answered Feb 03 '15 at 20:06

Std::vector is not just an array. It is STL type, whitch simulates dynamic array. What you are passing is simple 2D array like int arr[3][3]. To pass vector you need to change your function header to double function(vector< vector<int>> &vec)(or maybe double function(vector< vector<int>> vec) - depends on what you want to do)

Passing a multidimensional vector (matrix) to a Function in C++

3 Answers3