Adding words from a text file to a vector c++

I am trying to add each word from a file to a vector but if I make the size of the vector (500) and I only have 20 words in the file. The size of the vector is still considered 500. How do I fix this?

Am I doing this a bad way? Could this be made simpler?

void loadFile(string fileName)
{
    vector<string> fileContents(500);
    int p = 0;
    ifstream file;
    file.open(fileName);
    if (!file.is_open()) return;

    string word;
    while (file >> word)
    {
        fileContents[p] = word;
        p++;
    }

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