Pass multiple arrays of objects to a function

Question

The error that im getting is randm.cpp:42:52: error: no matching function for call to ‘Neuron::activationFunc(double&, double&)’ neu.activationFunc(feature[2][4], predicted[2][1]);

Is it possible to pass arrays or will i have to find another way of doing it? Here is my code. Its been a few years since i used classes so im a tad bit rusty.


#include <fstream>
#include <sstream>
#include <iostream>
#include <cstdlib>
using namespace std;

int correct = 0;

class Neuron {
    //double (&features)[150][4];

    public:
    double alpha = 0.5;
    double w1 = 1.0;
    double w2 = -1; 
    double w3 = 0.5;
    double w4 = 0;
    double x = 0;
    int theta = 1;
    int hardLim = 0;
    int track = 0;
    //void testClass();
    void activationFunc(double feature[2][4], double predicted[2][1]);

};
void Neuron::activationFunc (double feature[2][4], double predicted[2][1]) {
    for (int i = 0; i < 2; i++) {
        x = (w1*feature[i][0]) + (w2*feature[i][1]) + (w3*feature[i][2]) + (w4*feature[i][3]) + predicted[2][1];
        cout <<"\n X value is: " << x << endl;
    //hardLimit(x);
    //track = i;
    }

}

int main(int argc, char* argv[])
{
    //feature = col 1-4, predicted = col 5
    double feature[2][4]={1,2,3,4,5,6,7,8};
    double predicted[2][1]={4,5};
    Neuron neu;
    neu.activationFunc(feature[2][4], predicted[2][1]);

}

Thanks. P.S. I know there are a few things in my code that arent used yet.

Put your arrays inside a struct, then pass the struct. `struct Feature { double value[2][4]; };` and `struct Predicted { double value[2][1]; };` — Eljay, Apr 14 '19 at 19:26
Possible duplicate of [Passing a 2D array to a C++ function](https://stackoverflow.com/questions/8767166/passing-a-2d-array-to-a-c-function) — francesco, Apr 14 '19 at 19:41
Turn on more warnings. You are accessing elements outside your array-bounds. `predicted[2][1]` — Ted Lyngmo, Apr 14 '19 at 19:43
`neu.activationFunc(feature[2][4], predicted[2][1]);` You are not passing a multi-dim array but you are only passing an element. to do so pass only the name of the array: `neu.activationFunc(feature, predicted);`. ` — Raindrop7, Apr 14 '19 at 19:52

score 1 · Answer 1 · answered Apr 14 '19 at 19:27

1

To make it compile you need to change this line:

neu.activationFunc(feature[2][4], predicted[2][1]);

so that it looks like this instead:

neu.activationFunc(feature, predicted);

answered Apr 14 '19 at 19:27

Elias

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Note that you omit the “array sizes” here because they would be subscripts instead (to pick a single element, although these are of course out of range). – Davis Herring Apr 14 '19 at 19:34

Raindrop7 · Answer 2 · 2019-04-14T20:09:25.297

You can pass the multi-dimension array by reference or by pointer:

Your method prototype should look like:

class Neuron {
    //...
    void activationFunc(double(&)[2][4], double(&)[2][1]);
};

And the definition:

void Neuron::activationFunc (double (&feature)[2][4], double (&predicted)[2][1]) {
    for (size_t i{}; i != 2; ++i) {
        x = (w1 * feature[i][0]) + (w2 * feature[i][1]) + 
            (w3 * feature[i][2]) + (w4 * feature[i][3]) + predicted[1][0];
        std::cout << "X value is: " << x << std::endl;
    }

}

And in main just pass the arrays names:

neu.activationFunc(feature, predicted);

There is an Undefined Behavior in your loop:

x = (w1*feature[i][0]) + (w2*feature[i][1]) + (w3*feature[i][2]) + (w4*feature[i][3]) + predicted[2][1];

predicted is an array of [2][1] dimension so the valid range is [1][0] not [2][1].

Pass multiple arrays of objects to a function

2 Answers2