C++ error: munmap_chunk(): invalid pointer - c++

Question

My issue I assume is with &line.at(0). I had an error with it before, but dereferencing it took away the error. I am not sure why that is, as I was under the impression that my getline function would return the first line (one integer value that is the size of an array to sort), and the next would be a string of integers, separated by a space, that you put into the array that you then sort.
/* This Program is the main entry point
* in order to call insertion_sort
*/
#include <insertion_sort.cpp>
#include <utils.hpp>
#include <iostream>
#include <fstream>
#include <sstream>
#include <stdlib.h>
using namespace std;
int main(int argc, char const *argv[])
{
/**
* YOUR CODE HERE
* 1. Check for the number of arguments.
* Only proceed if the number of argument is correct,
* We will only check for ./main [INPUT_FILE] [OUTPUT_FILE]
*
*/
if(argc == 3){
/**
* YOUR CODE HERE
* 2. Read the file [INPUT_FILE]
*
*/
ifstream fin;
ofstream fout;
fin.open(argv[1]);
if (!fin.is_open()){
return -1;
}
string line;
string line2;
getline(fin, line);
getline(fin, line2);
int size = atoi(&line.at(0));
int iterator = 0;
/**
* YOUR CODE HERE
* 3. Build IntSequence
*/
IntSequence unsorted_array;
unsorted_array.length = size;
unsorted_array.array = new int[unsorted_array.length];
for (unsigned int i = 0; i < line2.length(); i++){
if (&line2.at(i) != " "){
unsorted_array.array[iterator] = atoi(&line2.at(i));
iterator += 1;
}
/**
* YOUR CODE HERE
* 4. Run Insertion Sort
*/
insertion_sort(unsorted_array);
/**
* YOUR CODE HERE
* 5. Write the file into [OUTPUT_FILE]
*/
fout.open(argv[2]);
if (fout.is_open()){
for (unsigned int i = 0; i < unsorted_array.length; i++){
fout << unsorted_array.array[i] << " ";
}
} else {
return -1;
}
}
fin.close();
fout.close();
return 0;
} else {
return -1;
}
}

Answer 1

In this line it seems that you are comparing a char * to another char *.
if (&line2.at(i) != " "){
I think that you intended to compare a char to a char instead, in other words check that the current character is not a space to then convert it to an integer.
if (line2.at(i) != ' '){
Otherwise your expression inside your if statement would likely return true even when you didn't count on it returning true, potentially overflowing your int array due to adding duplicate integers, since atoi ignores whitespace.