map /set iterator not incrementable

[masterinex]

hello,

i have this code. when i run it i get a runtime error: map /set iterator not incrementable on line 209. I am not sure why but when i check it2 under watchlist when it crashes it already points at "end".

I can't think of why that happens, because i have defined it2 as a local variable.

argv[1] is just a txt file with some random numbers in it.

  #include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <locale>
# include <algorithm>
# include <regex>
# include <list>
#include <map>
#include <set>


using namespace std;


template <typename T>

void print(T& c)
{
	cout << "Here is the dataset: ";

	for (auto x : c)
	{
		cout << x << " ";
	}


	cout << endl;

}



template <typename T>
void printmap(T& c)
{
	cout << "here is the map\n";

	for (auto p : c)
	{
		cout << p.first << "  " << p.second << endl;
	}

	cout << endl;


}




int main(int argc, char* argv[])
{
	//1. Read in the filename and open an input filestream
	ifstream inFile(argv[1]);
	//Test for success
	if (!inFile)
	{
		cerr << "Input file opening failed.\n";
		return EXIT_FAILURE;
	}

	//2. Get the numbers  from the file and store in a vector

	vector<int> v;
	string word;
	while (getline(inFile, word))
	{
		// convert string word to a number 
		int number = stoi(word);

		v.push_back(number);

	}


	//Finished reading in file
	cout << "Finished reading in file!\n";

	inFile.close();

	list<int> l;

	l.insert(l.end(), v.begin(), v.end()); 


	/*
	cout << "\nThe list with vector elements added to the end:\n";
	for (auto p : l)
		cout << p << " ";
	cout << endl;
	*/

	print(l);




	set<int> set2(v.begin(), v.end());

	print(set2); 


	map< int, int> mFrequency;

	for (unsigned i = 0; i < v.size(); ++i)
	{
		//mFrequency[v[i]] =  10 ;

		//mFrequency[v[i]] += 1; 

		++mFrequency[v[i]];


	}


	cout << "print map mFrequency using function " << endl; 

	printmap(mFrequency);

	// print each container using iterators


	cout << "print each key and value using iterator " << endl; 
	
	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		cout << " mFrequency[i] = key " << (*it).first << "value" << (*it).second << endl;

		//cout << " mFrequency[i] = key " << it->first << "value" << it->second << endl;

	}



	int largest = 0; 

	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		//cout << " mFrequency[i] = key " << (*it).first << "value" << (*it).second << endl;

		if ((*it).second > largest)
		{

			largest = (*it).second; 

		}

		//cout << " mFrequency[i] = key " << it->first << "value" << it->second << endl;

	}

	cout << "times the most frequent number/s occurs is " << largest << endl;


	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		//cout << " mFrequency[i] = key " << (*it).first << "value" << (*it).second << endl;

		if ((*it).second == largest)
		{

			cout << "mode is " << (*it).first << " ";

		}

		//cout << " mFrequency[i] = key " << it->first << "value" << it->second << endl;

	}



	int cunique = 0; 

	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		//cout << " mFrequency[i] = key " << (*it).first << "value" << (*it).second << endl;

		if ((*it).second == 1)
		{

			++cunique; 

		}

		//cout << " mFrequency[i] = key " << it->first << "value" << it->second << endl;

	}

	cout << "number of unique numbers  is  " << cunique << endl; 




	int total = 0; 

	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		
	 ++total;

	}

	cout << "total number before removing odd numbers" << total << endl; 
	
	// erasing odd elements from the map 

	for (map<int, int>::iterator it2 = mFrequency.begin(); it2 != mFrequency.end(); ++it2)
	{
		// if the number is odd 
		if ((*it2).first % 2 == 1)
		{

			mFrequency.erase(it2); 
		}

	}

	cout << "map after erasing odd elments" << endl; 

	printmap(mFrequency); 


	int ceven = 0; 

	for (map<int, int >::iterator it = mFrequency.begin(); it != mFrequency.end(); ++it)
	{
		
		

		++ceven;
		

	}


	cout << "total number of elements after removing odd elements is  " << ceven << endl;






	for (list<int>::iterator it = l.begin(); it != l.end(); ++it)
	{ 

		cout << *it << " ";


	}

	cout << endl;


	//set<int>::iterator it

	for (set<int>::iterator it = set2.begin(); it != set2.end(); ++it)
		cout << *it << " ";

	cout << endl; 

	cout << "print set using reverse iterators" << endl;

	set<int>::reverse_iterator rit;

	for (rit = set2.rbegin(); rit != set2.rend(); ++rit)
		cout << *rit << " ";

	cout << endl;



	system("pause");

}

[Handy Andy]

Hello masterinex,

Include an example of your input file. It makes it easier to run your program.

Andy

[Peter87]

The iterator gets invalidated when you remove the element so you need to assign a valid iterator value to it before using it again. You can use the return value of the erase function which is an iterator to the element after the erased element.

it2 = mFrequency.erase(it2);

You also need to avoid incrementing the iterator after an element has been erased because otherwise the loop will skip elements that comes after an erased element. You can do that by moving the iterator increment inside an else part of the if statement.

for (map<int, int>::iterator it2 = mFrequency.begin(); it2 != mFrequency.end();)
{
	// if the number is odd 
	if ((*it2).first % 2 == 1)
	{
		it2 = mFrequency.erase(it2); 
	}
	else
	{
		++it2;
	}
}

[masterinex]

thanks Peter,

here is the input file :

4
21
28
17
14
10
27
10
16
23
21
17
25
11
12
9
28
4
4
4
4
4
4
4
4
9
9
99
99
99
99
99
99
99
99
99
99
99
9
9
9
9
9
9
4
18
9
4
9
21
30
27
12
13
12
13
218
273
97
254
344
240
132
363
72
326
48
315
152
268
432
188
61
141