vector<bool> erase iterator outside range expression

[globaltourist]

i am writing a rather simple program for huffman encoding and cant find out why this: "expression:vector<bool> erase iterator outside range" keeps appearing.
I have tested each part of the code separately and it works fine and started testing the methods in groups and found that the fault is in the following function:

.cpp

 void huffman_encoder::compressor::encode_characters(Node *root) {
	if (root->_left != NULL) {
		_character_code.push_back(0);
		encode_characters(root->_left);
	}
	if (root->_right != NULL) {
		_character_code.push_back(1);
		encode_characters(root->_right);
	}
	if (root->_character) { _character_table[root->_character] = _character_code; }
	_character_code.pop_back();
}

.h

/*in private access of class compressor*/
std::vector<bool> _character_code;
std::map<char, std::vector<bool> > _character_table;

Note:the root of the huffman tree that is passed to the function as a parameter "root" creates a correct tree and has been tested separately (works perfectly).
And no other functions use the parameters "_character_code" and "_character_table" and moreover are encapsulated from having access to these parameters so nothing outside the function above can manipulate them or the vector erase iterator.

[jlb]

Where exactly is your debugger telling you it encounters the problem?

Be careful of using erase with vector iterators, you may be invalidating the iterator you're trying to use.

[globaltourist]

happens in vc\include\vector in line:2829 my code doesn't have that much lines and i have not used erase at all only push_back or pop_back

[jlb]

What do you think pop_back() is doing?

The line you pointed out is in the include file, you need to backtrace until you are somewhere in your code.

[AbstractionAnon]

happens in vc\include\vector in line:2829

That's the runtime code for vector.

i have not used erase at all

vector::erase is implicitly called by vector::pop_back to remove the last element.

What happens root->left and root->right are both NULL? Presumably this would happen at the end of each branch of your tree. If both ->left and ->right are NULL, you skip lines 3 and 7. When you get to line 11, the _character_code vector is empty (nothing was pushed). You can't pop_back() from an empty vector.

[globaltourist]

Thank you so much for helping me find the problem! i was trying to fix it 3 hours.. and read a ton of material on why and when the expression happens yet with no success,, until you came in.
so i have modified the code line 11 from:

_character_code.pop_back();

to :

if (!_character_code.empty()) {
		_character_code.pop_back();
}

is it a good way to do so? or is there another way you would of recommend over it ?
(with this replacement it now works!)

[globaltourist]

now when i want to view its contents with this function:

void huffman_encoder::compressor::test() {
	std::map<char, std::vector<bool> >::iterator test_itr;
	for (test_itr = _character_table.begin(); test_itr != _character_table.end(); test_itr++) {
		std::cout << test_itr->first << ":" << test_itr->second << std::endl;
	}
}

it doesnt let me print test_itr->second and says this:

Error C2679 binary '<<': no operator found which takes a right-hand operand of type 'std::vector<bool,std::allocator<_Ty>>' (or there is no acceptable conversion) Huffman_compressor c:\users\user\documents\visual studio 2015\projects\huffman_compressor\huffman_compressor\file_compressor.cpp 6

NOTE:I FIXED AND POSTED IT IN A COMMENT BELLOW

[jlb]

You're trying to print a vector not a single element unless you have overloaded the output operator<< to print each element of the vector<bool>.

This won't solve the current issue, but have you considered using the "new" range based loop instead of the iterator notation?

for(auto& itr : _character_table)
{
    std::cout << itr.first << " : " ;
    for(auto& it : itr.second)
        std::cout << it << " "; // Print out the vector<bool> elements.
    std::cout << std::endl;
}

[globaltourist]

well i still dont know how to use auto il overload operator << its not a problem

[jlb]

What don't you understand about using the ranged based loops? They greatly simplifies using iterators as shown in my snippet. By the way my snippet should properly print out your _character_table.

The auto keyword, since C++11, tells the compiler to automatically detect the proper type using type deduction.

For example:

auto i = 650; // Should automatically detect that i is an integer.
auto j = 6.5; // Should automatically detect that j is a double.
auto k = 6.5f; // Should automatically detect that k is a float, because of the 'f' specifier. 

[E0p9LyTq]

Range-based for statements (and static assert):
http://www.learncpp.com/cpp-tutorial/b-3-range-based-for-statements-and-static_assert/

Range based for loops are a very powerful C++11 tool, you should learn to use them.

C++11 added some new data types you might want to look at:

Long long, auto, decltype, nullptr, and enum classes
http://www.learncpp.com/cpp-tutorial/b-2-long-long-auto-decltype-nullptr-and-enum-classes/

[globaltourist]

i finally managed to solve the problem with printing the contents as they are in a map (char,std::vector<bool>) and wanted to post the code so that other people who come across the problem can modify it for their needs:

void huffman_encoder::compressor::test() {
	std::map<char, std::vector<bool> >::iterator test_itr;
	std::vector<bool>::iterator i;
	for (test_itr = _character_table.begin(); test_itr != _character_table.end(); test_itr++) {
		std::cout << test_itr->first << ":";
		for (i = _character_table[test_itr->first].begin(); i != _character_table[test_itr->first].end(); i++) {
			std::cout << (*i);
		}
		std::cout << std::endl;
	}
}

Note: overloading operator << isn't needed with this method.

+ thanks for the links above il look into them as soon as i finish my current project