Populating an array of stucts

[rottmanj]

I am working on an application where I need to store data in an array of stucts. The issue that I am running into is that I do not know the length of the array, I will never know the max length of the array. So I am kind of stuck at an point to where I am not sure exactly what to do.

Here is the code that I am currently working with. Any help with this is greatly appreciated.

Struct: (N_SOURCES is defined, but with out a length)

        struct ClassData {
        	
        	std::string rSource;
        	std::string cName;

        } *ResourceData[N_SOURCES];

Code I am using to populate/test output:

        MetadataResourceList::iterator i;
        for (i = resources.begin(); i != resources.end(); i++)
        {                   
            MetadataResource * resource = *i;
            
            string resourceName = resource->GetResourceID();
                
            MetadataClassList classes =	
                metadata->GetAllClasses(resourceName);
            MetadataClassList::iterator i;
            for (i = classes.begin(); i != classes.end(); i++)
            {
                MetadataClass * aClass = *i;
                
                if(aClass->GetStandardName() != ""){
                	ResourceData[i].rSource = resourceName;
                	ResourceData[i].cName = aClass->GetStandardName();
                }
            }
        }
        
        cout << "Resource Name: " << ResourceData[0].rSource << " Class Name: " << ResourceData[0].cName << endl;

[helios]

N_SOURCES is the length of the array.

I'm confused about this: ResourceData[i]
i is an iterator. How can you use it to index an array?

I don't think this string comparison is correct: (aClass->GetStandardName() != "")

[rottmanj]

N_SOURCES was from a previous bit of testing that I was doing. Due to the fact that I will never know the max length of the array, I need to find a way to create a dynamic array of structures.

The reason I used i was to create the index for the array. IE on the first iteration i = 0 and the first index in the array would be 0.

As for the sting comparison it is just temporary until I get the structure populated and for ease of display during testing.

[Mythios]

For an array though all you would need is
something like off the top of my head

int *arraySize = new int;
std::cin >> *arraySize;

int *myArray = new int[arraySize];

for(int i = 0; i < arraySize; i++)
{
	myArray[i];
}

[rottmanj]

That is essentially what I have done by doing this.

        struct ClassData {
        	
        	std::string rSource;
        	std::string cName;

        }*ResourceData[resources.size()];

resources.size() gives me the total number of resources I will have. Now, the issue is this. When I try to populate the array of structures with the code below. I always get this error.

no match for ‘operator[]’ in ‘ResourceData[i]’

[helios]

iterators are not integers. something.begin()!=0

a dynamic array of structures

http://www.cplusplus.com/reference/stl/vector/

no match for ‘operator[]’ in ‘ResourceData[i]’

I'm not sure about that error. ResourceData is a 'ClassData **', to it should interpret the [] as the common offset operator, not as an overloaded operator.

[rottmanj]

I got it all figured out.

Here is what I did.

        struct ClassData {
        	
        	std::string rSource;
        	std::string cName;


        }*ResourceData;
        
        
        ResourceData = new ClassData[resources.size()];

Then I can use something like this

int k = 0;

forloop
                    ResourceData[k].rSource = resourceName;
                    ResourceData[k].cName = aClass->GetClassName();
endfor

[rottmanj]

I do have one other question. What would be the best way to get the length of the array of structures. I have tried using sizeof(), but for some reason no matter how many indexes there are I always end up with the value of 4.

[jsmith]

You have to store the size somewhere if you dynamically allocate it like above.

[helios]

sizeof is only giving you the size of the pointer in bytes (32-bits/8=4).

[rottmanj]

After spending some time working on this, I have come to the conclusion that this may not be the preferred way to handle this. After a bit of looking into other ways I could do this. I have realized that a multidimensional array would better suit what I am trying to do.

With a bit of testing I have come up with this simple vector array.

	vector< vector<int> > vec;

	for (int i = 0; i < 3; i++) {
	    vector<int> row;
	        row.push_back(i);
	    vec.push_back(row);
	}
	
	for(int k = 0; k < vec.size(); k++){
		for(int l = 0; l < vec[k].size(); l++){
			cout << "Resource : " << vec[k][l] << endl;
		}
	}

This gives me the output of.

Resource : 0
Resource : 1
Resource : 2

The one thing I can not figure out is how to create a subvector of "Resource" so I would wind up with an output something like this.

Resource : 0
	Class: 0
	Class: 1
Resource : 1
	Class: 0
	Class: 1
Resource : 2
	Class: 0
	Class: 1

[helios]

What do you mean? You already figured out the vector<vector<T> >.

[rottmanj]

Well what I am trying to do is create a multidimensional vector array where each parent array element can have multiple children array elements. My last code block in my previous post was some what of an example.

Here is a better one.

If I have the parent array element 0 how would I write it so that 0 could have multiple children array elements. Right now if I want to access the data in the current implementation that I have I could do something like below. But this however would only give me the parent element.


cout << vec[0][0] << endl;

If I wanted to access the child array element I would access it something similar to this.

cout << vec[0][0][0] << endl;