Problem with vectors

[confused23]

I tried looking for an answer to my problem here, but couldn't get any. Hence posting this here.

I have a class stream, with a private member variable vector<int> request_nodes. It also has a member function add_requested_nodes which simply does the following:
void stream::add_requested_nodes(int t)
{

request_nodes.push_back(t);

}


Now, when I do a stream_object.add_requested_nodes(integer value) from my main function; the request_nodes is not reflecting the changes when I access the same stream object later in the main function.

I have not used pointers anywhere in the classes.

Does this mean that I should declare request_nodes as a vector<int*> ?

[confused23]

By the way, I am coding in Microsoft Visual C++

[m4ster r0shi]

Does this mean that I should declare request_nodes as a vector<int*> ?

No, you are doing this right, it should be vector<int>

I can't locate the problem with only this much of information. Can you post some code relative to the points in main where (1) you add the nodes and (2) you access the stream object to view the nodes? I mean, not only the code in main where you call the functions writing to/reading from the stream but the code inside these functions as well. Your add_requested_nodes seems to be fine but maybe the problem is located in reading the stream object...

[confused23]

I dont think that is the case since when I use breakpoints, the visual c++ debugger shows me that the vector of the stream is empty.

But this is how I am reading the vector:
stream_object.getrequest_nodes(), where this function is defined as

vector<int> stream::getrequest_nodes()
{

return request_nodes;

}

There is some problem in using vectors this way I think, since some other class having a vector is behaving similarly. I tried overloading the = operator but that did not help too.

[confused23]

This is where I add the nodes in the main function:

for(int j=0;j<REQ_NUM;j++)
{

rand_num=(rand()%num_stream) + 1;
g.add_stream_requested(rand_num);
temp=((rand_num-1)/4) +1;
node_source=nodes.at(temp-1);
stream s=node_source.find_stream(rand_num);
s.add_requested_nodes(g.getnodeId());

}


This is where I read the stream again:

for(j=streamList.begin();j!=streamList.end();j++)
{


stream s=*j;
s.setrequestSize(s.getrequest_nodes().size());
globalRequest += s.getrequestSize();
sorted_s.push_back(s);

}


The s.getrequest_nodes().size() always turns out to be 0, since the request_nodes are not set properly.


Breakpoints and the debugger tells me that the problem lies in the point I explained in the first post.


Thanks in advance!

[confused23]

Following http://www.cplusplus.com/forum/beginner/12302/ I also introduced a copy constructor in stream but to no help:

stream::stream( const stream& that )
{

stream_id=that.stream_id;
source_id=that.source_id;
required_BW=that.required_BW;
request_nodes=that.request_nodes;
request_size=that.request_size;
stream_tree=that.stream_tree;
}



none of the above fields is a pointer.

[confused23]

I figured out the problem. I am making copies of the stream everywhr which doesnt give me direct access to the desired object.

Problem of switching from Java to c++ :)

[m4ster r0shi]

Try modifying the part you add the nodes like this and see if it works.

for(int j=0;j<REQ_NUM;j++)
{

rand_num=(rand()%num_stream) + 1;
g.add_stream_requested(rand_num);
temp=((rand_num-1)/4) +1;
node_source=nodes.at(temp-1);
stream & s=node_source.find_stream(rand_num); //<- here add '&' between 'stream' and 's'
s.add_requested_nodes(g.getnodeId());

} 

You see, what stream s=node_source.find_stream(rand_num); does is that it finds the stream you want to modify and the create a new stream object, s, and then copy the stream you want to modify to s. Consequently, no matter what you do to s, the object you want to modify won't be affected...

However, if you declare s like stream & s=node_source.find_stream(rand_num); (that is you declare s as a 'reference' to the object returned by node_source.find_stream(rand_num);), what you effectively do is say to your compiler: "I want s to be a nickname for the object returned from node_source.find_stream(rand_num);, so that whatever changes I do to s actually modify that object".

But, there's one more thing you have to check. node_source.find_stream(rand_num); must also return a reference to the desired object. Consider the following... I want you to notice that you can only modify a variable when there is a 'reference chain' from the target variable all the way to the variable you use for the modification.

#include <iostream>
using namespace std;

class MyClassRef
{
	public:
	MyClassRef(int v){value=v;}
	int & getValue() {return value;} //notice the '&' here
	
	private:
	int value;
};

class MyClassVal
{
	public:
	MyClassVal(int v){value=v;}
	int getValue() {return value;} //no '&' here

	private:
	int value;
};

int main()
{
	MyClassRef mcr(5);
	MyClassVal mcv(10);

	cout << "MyClassVal" << endl;
	
	cout << mcv.getValue() << endl;
	
	//trying to modify...
	int var_val=mcv.getValue();
	var_val=123;
	
	cout << mcv.getValue() << endl;
	//nope... neither var_val is a reference nor getValue() returns a reference...

	//trying to modify...
	int & var_ref0=mcv.getValue();
	var_ref0=123;	
		
	cout << mcv.getValue() << endl;
	//nope... var_ref0 is a reference but getValue() does not return a reference...

	cout << "MyClassRef" << endl;
	
	cout << mcr.getValue() << endl;
	
	//trying to modify...
	var_val=mcr.getValue();
	var_val=123;
	
	cout << mcr.getValue() << endl;
	//nope... because even though getValue() returns a reference, var_val isn't a reference

	//trying to modify...
	int & var_ref1=mcr.getValue();
	var_ref1=123;	
		
	cout << mcr.getValue() << endl;
	//yeap! getValue() returns a reference and var_ref1 is a reference

	cout << "hit enter to quit..." << endl;
	cin.get();
	return 0;
}

[m4ster r0shi]

lol, I just saw your last post...