How to read a 2d triangle array from txt file? - c++

Question

I want to read 2d triangle array from a txt file.
1
8 4
2 6 9
8 5 9 6
I wrote this code. At the end I wanted to print it out if I got the array right. When I run it it does not print the array, but in debug it prints. So there is a problem, but I cannot find it. Sometimes it gives segmentation fault, but I dont understand.
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
int main() {
std::ifstream input_file("input_file.txt");
int size{1};
int **arr = (int**)malloc(3*sizeof(int));
int *lineArr = (int*) malloc(size*sizeof(int));
int temp{};
int index{};
while(input_file >> temp){
lineArr[index] = temp;
index++;
if(index == size){
index = 0;
arr[size-1] = new int[size-1];
for(int i{}; i<size; i++){
arr[size-1][i] = lineArr[i];
}
size++;
lineArr = (int*) realloc(lineArr, size*sizeof(int));
}
}
input_file.close();
for(int a{}; a<size-1; a++){
for(int j{}; j<=a; j++){
std::cout << arr[a][j] << " ";
}
std::cout << std::endl;
}
return 0;
}

Answer 1

You can just use vector instead of malloc. Like this:
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
#include <vector>
using namespace std;
int main() {
ifstream input_file("input_file.txt");
vector<string> numbers;
if (input_file.is_open()) {
string line;
while (getline(input_file, line)) {
numbers.push_back(line);
}
input_file.close();
}
for (vector<string>::iterator t=numbers.begin(); t!=numbers.end(); ++t)
{
cout<<*t<<endl;
}
return 0;
}