Vector iterators are from different containers error

Question

0.00/5 (No votes)

See more:

Hello, I am trying to concat vectors when I get data from cable in my while loop. I search for

C++

copy

method in C++ array a lot and I saw examples like my code which are supposed to run correct, however I am getting error as in title. I put breakpoints and I observed;

copy(GetIntArrayFromCharArray(vec).begin(), GetIntArrayFromCharArray(vec).end(), it+intData.size());

in this line first time it calls

GetIntArrayFromCharArray

was okay, then it calls it for

.end()

then error shows up. I also watched iterator, it is not empty. I couldn't figure out what should I do?

(PrevFrameFragmentNo and other variables are just to trace frame and segments in UDP packet data.)

What I have tried:

THIS CODE PIECE IS IN WHILE LOOP, TAKES DATA TO BUFFER

//char buf ----> vecor<char> vec
		int n = sizeof(buf) / sizeof(*buf);//number of elements
		vector<char> vec(buf, buf + n);

		 


		if (FrameFragmentNo == 1)// First fragment
		{
			intData = GetIntArrayFromCharArray(vec);
			PrevFrameFragmentNo = FrameFragmentNo;
		}
		else if (FrameFragmentNo <= TotalFragmentCount)  // Other Fragments
		{
			vector<uint16_t> concatAry;
			std::vector<uint16_t>::iterator it;

			
			
			
			concatAry.assign(intData.begin(), intData.end());
			

			it = concatAry.begin();
			//PROBLEMATIC LINE IS HERE
			copy(GetIntArrayFromCharArray(vec).begin(), GetIntArrayFromCharArray(vec).end(), it+intData.size());

			
			intData = concatAry;
			PrevFrameFragmentNo = FrameFragmentNo;
			count++;
		}

THIS CODE IS GetIntArrayFromCharArray() METHOD

vector<uint16_t> GetIntArrayFromCharArray(vector<char> arr)
{
	
	if ((arr.size() % 2) == 1)
		arr.resize(arr.size()+1);
	


	vector<uint16_t> intArray;

	for (int i = 0; i < arr.size(); i += 2)
		intArray.push_back((uint16_t)((arr[i] << 8) | arr[i + 1]));

	return intArray;
}

Posted 5-Sep-19 22:15pm

Danny96

Updated 5-Sep-19 22:22pm

v3

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Stefan_Lang · Accepted Answer · 2019-09-05T22:22:00

Solution 1

The function GetIntArrayFromCharArray creates a copy, therefore your calls to begin() and end() refer to two different arrays! This is reflected literally in the error message - all you need to do is read and understand it. ;-)

[..] (cut away revised parts of the solution - see below)

P.[...]S.:
[...]
Sorry, I need to revise my solution a third time:
It seems you are trying to append multiple converted int arrays in a loop: the first time you simply call

GetIntArrayFromCharArray

, and that's fine. Inthe following loop iterations, you convert the char array and try to append it to the existing int array.

As for the solution you're looking for, the first thing you need is a local variable to hold the converted int array, as pointed out above, and then you need append(), like this:

C++

auto myIntArray = GetIntArrayFromCharArray(vec);
concatAry.append(myIntArray.begin(), myIntArray.end());

The copy() function can be used only for the purpose of copying data to a location that is already allocated. Your concatAry however is only large enough to hold it's existing elements, therefore you need to use append() instead. Alternately you could use resize() first, but why use two function calls when you can do it in one? ;-)

Posted 5-Sep-19 22:22pm

Stefan_Lang

Updated 6-Sep-19 0:34am

v4

Comments

Danny96 6-Sep-19 4:29am

you are right, I correct it but it gives "can not seek iterator after end" error now, iterator is not empty, I don't understand why compiler struggles with iterator, do you have an idea? :(

phil.o 6-Sep-19 4:42am

Most probably, you are trying to copy the source array into destination array, and destination array is too small to host the data you are trying to fit in.
Why don't you use debugging for that kind of issue?

Danny96 6-Sep-19 4:46am

I am already on debug mode and source is bigger than destination array I already know but they are vectors, it shouldn't be a problem I thought

phil.o 6-Sep-19 4:51am

It is not a problem when you use the right push_back method to add elements at the end of the vector.
Is is a problem, though, when you deal directly with iterators. Iterators are pointers; they point to a memory address in application's space. If you manipulate the pointer arithmetically, you may end up referencing a memory address which is beyond the area assigned to the vector. This is a typical buffer overflow.

Stefan_Lang 6-Sep-19 6:11am

Iterators are not pointers, although they behave very similarly. But that is not the problem here anyway. I've modified my solution with further insights and advice.

Stefan_Lang 6-Sep-19 6:15am

You are right that std::vector can automatically resize to fit it's needs, but you need to use the appropriate methods. copy() does not resize, it attempts to overwrite memory in a location that's already reserved. OTH, push_back(), insert(), and append() all adjust the allocated memory to fit the added data.

Stefan_Lang 6-Sep-19 5:52am

Ok, I hadn't checked the details of your code. I didn't spot that you already had created a copy and stored it in intData. In that case, of course the first line of the code I posted is not needed, and the second line should be changed to use intData, instead of myIntArray.

If you read my explanation carefully, it might occur to you that intData is a different copy than myIntArray from the code segment I posted above. Therefore it's not sensible to operate on these two different objects - whatever you do with one object, is not reflected in the state of the other object!

Danny96 6-Sep-19 7:10am

I understand, thank you