How to pass from array to vector - c++

Question

I'm new in c++ programming and I'm trying to understand better the differences between array and vector. In my program I've got a class Graph with some arrays as private members. The class has a method that use these arrays to implement the Prim's algorithm for minimum spanning tree. I took the algorithm from this page and changed it for my program.

I am now asked to use vectors instead of arrays so I would like to know:

How many things do I really have to change? The declaration and the constructors, ok. But the cycles, the initializations. Do I have to change everything? The program works anyway. Is it so important to use vector's function?

Show us some code and indicate which array should be converted to a vector. — masoud
– masoud, Commented Nov 11, 2013 at 14:52
Hard to say without seeing any code. I would change the declarations first and see how it goes from there. — john
– john, Commented Nov 11, 2013 at 14:54

igleyy · Accepted Answer · 2013-11-11 18:58:15Z

1

If you want to stick with current implementation but you would like to experiment with vectors you could populate vector with array data this way:

vec.assign(arr, arr + arr_size);

answered Nov 11, 2013 at 18:58

igleyy

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1 Comment

ca250802 Over a year ago

This worked! This is the so-called iterator construction a vector from arrays - the iterator constructor can also be used to construct from arrays

Bruce Dean · Accepted Answer · 2013-11-11 18:55:09Z

0

I took a look at the code at your link above and spotted quite a few places where STL vectors can be used rather than the arrays that are defined.

For example, below is an example of how to replace a couple of the arrays with vectors, and then initialize their values:

#include <iostream>
#include <limits>
#include <vector>

// Number of vertices in the graph
static const int V = 5;

int main()
{
    // Rather than use:
    // int key[V];
    // bool mstSet[V];

    // You could setup STL vector containers:
    std::vector<int> key;
    std::vector<bool> mstSet;

    // Next, initialize:
    for (size_t i = 0; i < V; i++) {
        key.push_back(INT_MAX);
        mstSet.push_back(false);
        std::cout << key[i] << "; " << mstSet[i] << std::endl;
    }

    return 0;
}

edited Nov 11, 2013 at 18:55

answered Nov 11, 2013 at 15:21

Bruce Dean

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2 Comments

Manu343726 Over a year ago

<limits.h> is C, the C++ equivalent is <limits>. Don't use #defines, use const. Avoid other C libraries like stdio. Avoid using namespace std

Bruce Dean Over a year ago

@Manu343726, your exactly right. I cleaned up the code to better illustrate good C++ practice. Thanks for your comments.

Paul Evans · Accepted Answer · 2013-11-11 15:06:51Z

0

It should be very simple to switch from arrays to a vector. You could initialise the vector with the size of your array and fill it with 0 elements:

vector<YourType> v(size_of_array, YourType(0));

and then use v more or less as you used your array, i.e.:

v[x] = YourType(y);
// ....
f(v[z]);

etc

answered Nov 11, 2013 at 15:06

Paul Evans

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