Calling Functions From Main in C++

Question

I'm trying to call my Dijkstra() method from Main.cpp.

#include <iostream>
#include "Alg.h"

int main(int argc, char **argv) { 

    Alg::dijkstra();
    return 1; 
}

It is delcared in my Alg class in my header file:

#ifndef Alg_
#define Alg_

#include <iostream>
#include <stack>

using namespace std;

 class Alg
{
    public:
        void tracePath(int x);
        void output();
        void printArray();
        void Initialize();
        void dijkstra();
        int current, mindex;
        int distanceArray[7][7]; //2D array to hold the distances from each point to all others
        int d[6]; //Single distance array from source to points
        int p[6]; //Array to keep predecessors 
        int copyD[6]; //Copy of d[] used for sorting purposes in tracePath()
        int order[6]; //Contains the order of the nodes path lengths in ascending order

}; //End alg class

#endif

And implemented in my Alg.cpp file:

void Alg::dijkstra() { 

    //Create Map
    Initialize();

    for(int i=0; i<5; i++)
    { 

        current=1;

        while(current!=6)
        {
            //Iterate through and update distances/predecessors
            //For loopt go through columns, while current iterates rows
            for(int j=1; j<7; j++)
            {
                //Check if distance from current to this node is less than
                //distance already stored in d[j] + weight of edge

                if(distanceArray[current][j]+d[current]<d[j])
                {
                    //cout<<"Previous distance to "<<j<<" was "<<d[j]<<" from "<<p[j]<<endl;
                    //cout<<"New smaller distance is "<<distanceArray[current][j]+d[current]<<" from "<<current<<endl;
                    //Update distance
                    d[j] = distanceArray[current][j]+d[current];
                    //Update p
                    p[j] = current;
                }    
            }
            //Go to next row in distanceArray[][]
            current++;
        } //End while


    } //End for
    //printArray();

    output();
} //End Dijkstras

Calling it as Alg::dijkstra() gives error: cannot call member function ‘void Alg::dijkstra()’ without object, and calling it simply as dijkstra() gives error: ‘dijkstra’ was not declared in this scope.

Previously, I had all of these methods defined in my Main.cpp file and it worked just fine (see here: http://pastebin.com/67u9hGsL), I'm missing something here now that I've separated it. dijkstra() needs no input, and all of it's other functions are in the header/cpp files with it.

How can I successfully call dijkstra() from main?

You need an instance of that class. But if you don't, make it a namespace, perhaps, or make the function static. — nullpotent, Dec 03 '13 at 23:22
Bad duplication of own question: http://stackoverflow.com/questions/20362973/static-functions-in-c. — , Dec 03 '13 at 23:31

score 2 · Accepted Answer · answered Dec 03 '13 at 23:22

2

You need to make an instance of the class:

Alg a;
a.dijkstra();

or make dijkstra a static method in the class:

static void dijkstra();

for simplicity in your implementation I would recommend the first option.

answered Dec 03 '13 at 23:22

pippin1289

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This compiles, yet gives no print output like dijkstra() is meant to. Is this a result of calling it on the instance? Or should it function fine regardless? @pippin1289 – Ladybro Dec 03 '13 at 23:29
@user3063527 It should function fine. There is some other error in your algorithm problem that prevents the output. – pippin1289 Dec 03 '13 at 23:33
@user3063527 its likely a problem in `output()` – pippin1289 Dec 03 '13 at 23:34

Calling Functions From Main in C++

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