Vector Struct

**Elysia** · 12-21-2011

What errors do you get?

**Khadafi** · 12-21-2011

i have attached a screenshot of the errors i am getting

thanks

**Elysia** · 12-21-2011

compareByCost is a function, so move it outside main or whatever other function you have it placed inside.

**Khadafi** · 12-21-2011

Hi, when i move it outside, it says that WEdge is undefined.
do i also need a declaration of the function at the top as it is a function?

thanks

**hk_mp5kpdw** · 12-21-2011

#1

A suggestion, implement a constructor for your WEdge struct:

Code:

struct WEdge
{
    int From;   // an array for u points
    int To; // an array for v points
    int Cost;   // an array for w points
    WEdge(int f = 0, int t = 0, int c = 0) : From(f), To(t), Cost(c) {}
};

Then your vector/pushback code (post #5) can be simplified:

Code:

vector<WEdge>myEdges;
     
myEdges.push_back(WEdge(1,2,5)); // add edge to vector
myEdges.push_back(WEdge(2,6,10)); // add edge to vector
myEdges.push_back(WEdge(3,4,7)); // add edge to vector

#2

I cant seem to print out data from the vector now, e.g. i have tried

Code:

for(int i=0; i<myEdges.size(); i++)
{
	cout << "data" << i << " Is: " << myEdges[i] << "\n";
}

how would i access edge1 data such as the To, From, Weight that is held in the vector myEdges?

You could do a couple things to access the elements. Remember myEdges is the vector of WEdge objects. Therefore, myEdges[i] is an element of this vector, i.e. a WEdge object. A WEdge object has a From/To/Cost member and so to access it you could do this:

Code:

for(int i=0; i<myEdges.size(); i++)
{
	cout << "data" << i << " Is: " << myEdges[i].From << ' ' << myEdges[i].To << ' ' << myEdges[i].Cost << "\n";
}

A better method however might be to look at overloading operator<< which is the stream insertion operator (writes to a stream). You could then do exactly what you had tried above since then the compiler would know how to write a WEdge object using <<. An example:

Code:

struct city
{
    std::string name;
    int population;
    city(std::string n,int pop) : name(n), population(pop) {}
};

std::ostream& operator<<(std::ostream& os, const city& rhs)
{
    return os << "City name: " << rhs.name << "\nPopulation: " << rhs.population;
}

...

city my_city("San Diego",1000000);

std::cout << my_city << std::endl;

Should output something like:

Code:

City name: San Diego
Population: 1000000

**Elysia** · 12-21-2011

Originally Posted by Khadafi

do i also need a declaration of the function at the top as it is a function?

Yes.
Also, though this isn't necessary, you may find this interesting:
C++11 - Lambda Closures, the Definitive Guide - Cprogramming.com
It is related to your problem. In a way.

**Khadafi** · 12-21-2011

thanks hk_mp5kpdw, i have done that to simply push_back, thats great =) thanks

Elysia...i am not sure what to do, i have put the function outside, and put a function header, but it keeps saying that WEdge is undefined, would i need to put the WEdge struct outisde aswell.
Why do i need to say WEdge in the bool code as we are comparing things inside the vector. ahh im so confused, sorry for all the silly questions.

**Elysia** · 12-21-2011

Show your code.
sort is comparing elements inside the vector, but will call upon your comparison function to see which one of two elements in the lesser one.

**Khadafi** · 12-21-2011

Code:

bool compareByCost (const WEdge &lhs, const WEdge &rhs)
	{
	return lhs.wCost < rhs.wCost;
	}

**Elysia** · 12-21-2011

Ah, put your struct before the compareByCost function declaration.
Also change

"for(int i=0; i<myEdges.size(); i++)"
to
"for(std::size_t i=0; i<myEdges.size(); i++)"

And similarly for the other for loop. That will eliminate warnings (which you should pay heed to!).
The size() function does not return an int.

**Khadafi** · 12-21-2011

thats what i was thinking but i remember someone telling me that you shouldnt make things global like that.
but thanks it all seems to be working, i really appreciate everyones help so much

thanks =)

**Elysia** · 12-21-2011

What you should avoid are global variables.

**Khadafi** · 12-21-2011

oh okay.

thanks very much.

**Elysia** · 12-21-2011

No problem. Check back if you have further problems.

Thread: Vector Struct

Thread Tools

Search Thread

Display

Similar Threads

Vector of a struct containing another vector

Class/Struct in a Vector...

Using a vector of pointers in a struct...HELP!

struct + vector = fun

vector<struct>