String splitting code from cookbook using more memory than allocated; An edX or code problem?

Question

I am taking a course in c++ programming by IBM through edX. A majority of the program are hands-on exercises where one writes code to meet specifications, for a desired output given input, with samples of both provided. An online compiler is used to execute and evaluate the code.

I took code from a cook-book to split a string. As far as I can tell, the code should work. When I compile it though, the compiler runs out of memory, which I believe has 512 mb allocated to it. As the compiler is a service provided, I cannot allocate memory to it or change any settings. It is also the compiler I am required to use for the course. I asked on the course discussion board why my code is causing problems, but I have had no responses. I would like to know if the problem is the compiler and platform, or if I have a problem in my code.

I pared down the code to just what is needed for splitting a string, which is causing the memory allocation problems.

#include <iostream>
#include <string.h>
#include <vector>
#include <functional>

using namespace std;
void split(const string &s, char c, vector<string> &v)
{
    string::size_type i = 0;
    string::size_type j = s.find(c);

    while (j != string::npos)
        v.push_back(s.substr(i, i - j));
    i = ++j;
    j = s.find(c, j);

    if (j == string::npos)
    {
        v.push_back(s.substr(i, s.length()));
    }
}

int main()
{
    // Fill the code here
    //  Strings
    string prompt1 = "Enter name: ";
    string prompt2 = "Enter roll number: ";
    string prompt3 = "Enter Date of Birth [DD MM YY] format: ";

    vector<string> v;
    string s = "Something To Put Here";

    split(s, ' ', v);

    for (int i = 0; i < v.size(); ++i)
    {
        cout << v[i] << endl;
    }

    return 0;
}

So, is it the code or is it the platform?

Answer 1

The following code causes an infinite loop.

while (j != string::npos)
        v.push_back(s.substr(i, i - j));

Since the while loop is not enclosed in braces, only the statement following the while loop is part of the loop. The variable j is not updated in the loop, it will never be equal to string::npos, causing an infinite loop.

Also, s.substr(i, i - j) is incorrect since i - j will give a negative length. It should be s.substr(i, j - i)

Following loop should work as expected

while (j != string::npos)
{
    v.push_back(s.substr(i, j - i));
    i = ++j;
    j = s.find(c, j);

    if (j == string::npos)
    {
        v.push_back(s.substr(i, s.length()));
    }
}