Question

I feel so lost trying to figure this out. I have my own data structure that I am planning on using vectors to avoid having to keep track of free space and reorginization that I would need to do if I used a simple array. I don’t don’t know if I’m just not initializing properly or what, but every assignment I do seems to just disappear into thin air.

Here is some simple code to illustrate what I’m talking about:

#include <vector>
#include <iostream>

using namespace std;

struct node
{
    int test_int;
    bool test_bool;
};

struct file
{
    vector<node> test_file;
};

int main()
{
    file myfile;
    int myint;

    cout << "Enter number: ";
    cin >> myint;

    myfile.test_file[0].test_int = myint;

    cout << "Number entered is: " << myfile.test_file[0].test_int << endl;

    return 0;
}

So basically it is a vector inside a struct. It seems that the normal ways to access a vector don’t seem to work, as in I can’t read or write anything to the vector however things like myfile.test_file.size() seem to work (as in they return a ‘0’ from a freshly created struct). Trying to access the index directly by myfile.test_file[0].test_int results in a runtime error of vector subscript out of range as if it isn’t actually there.

Am I not initializing it properly? This seems kind of ridiculous to me and I can’t understand why it wouldn’t work that way.

Edit:
Edited code to more clearly show behavior I’m referring to. This compiles but gives a runtime error vector subscript out of range

Answer 1

The edited version doesn’t work because you’re accessing an element past the end of the vector:

    myfile.test_file[0].test_int = myint;

Before you can do this, you need to either resize() the vector, or add an element using push_back():

    myfile.test_file.push_back(node());
    myfile.test_file[0].test_int = myint;