C++: Unhandled exception: std::out_of_range at memory location

Question

Currently learning C++ building a little program that takes in movie names, stores them in a vector and then outputs it based on user input. The problem is I made a function for displaying the movies list. Now every time I run that function I get this error:

Unhandled exception at 0x769DA842 in ConsoleApplication2.exe: Microsoft C++ exception: std::out_of_range at memory location 0x0113F674.

Here's the code:

#include <iostream>
#include <vector>

std::vector <std::string> movieList;
std::vector <int>::iterator it;

void AddMovie(std::string movie)
{
    movieList.push_back(movie);
}

void DeleteMovie(int i)
{
    movieList.erase(movieList.begin() + i - 1);
}

void ShowMovies()
{
    for (int i = 0; movieList.size() > 1; i++)
    {
        std::cout << movieList.at(i) << std::endl;
    }
}

int main()
{

    int i{ 0 };

    movieList.push_back("Inception");
    movieList.push_back("Peter Pan");
    movieList.push_back("Jaws");

    std::cout << "Delete movie: ";
    std::cin >> i;
    DeleteMovie(i);
    ShowMovies();

    
}

The error breaks at line

std::cout << movieList.at(i) << std::endl;

for (int i = 0; movieList.size() > 1; i++) will go on forever if there are at least 2 items in the list. You probably meant for (int i = 0; i < movieList.size(); i++) — 001
– 001, Commented Feb 9, 2021 at 18:56
Does this answer your question? What is a debugger and how can it help me diagnose problems? — Aykhan Hagverdili
– Aykhan Hagverdili, Commented Feb 9, 2021 at 19:01

Alberto Casas Ortiz · Accepted Answer · 2021-02-09 19:17:47Z

1

In the for loop, the condition movieList.size() > 1 is always true (if you have more than one movie in the list), so you are incrementing i beyond the size of the list, accessing to memory out of the range of the vector.

This example should work, since the variable i is only used in the body of the loop till it reach movieList.size() - 1 (as @user4581301 commented above, it is increased to movieList.size(), but that last value is not used in the loop body):

void ShowMovies()
{
    for (int i = 0; i < movieList.size(); i++)
    {
        std::cout << movieList.at(i) << std::endl;
    }
}

edited Feb 9, 2021 at 19:17

answered Feb 9, 2021 at 19:02

Alberto Casas Ortiz

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3 Comments

user4581301 Over a year ago

Alternative: for (const auto & val: movieList) {std::cout << val << std::endl; } Documentation on range-based for

user4581301 Over a year ago

Minor correction: the variable i is only incremented till it reach movieList.size() - 1: is not quite true. i is incremented to movieList.size(), but i reaching movieList.size() is the exit condition so movieList.size() - 1 is not used in the body of the loop. i goes out of scope immediately after reaching movieList.size() so the point is moot.

Alberto Casas Ortiz Over a year ago

@user4581301 you are right, it is incremented once more than I said, but not used in the loop.

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