为什么我的 vector::erase 调用会抛出“向量下标超出范围”？

Question

I'm writing a program that saves words from a .txt file in vector words , calculates how many words are there (num_elements) and prints these words randomly to the screen (no duplicates).

It all works fine up until rw.erase line, which just spits out the error "vector subscript out of range".

Why is my erase call throwing "vector subscript out of range"?

#include <iostream>
#include <string>
#include <fstream>
#include <Windows.h>
#include <direct.h>
#include <filesystem>
#include <time.h>
#include <random>
#include <vector>
#include <iterator>
#include <algorithm>

using namespace std;

void path_to_main_dir() {
    string path = "C:/Randomizer/";
    for (const auto& entry : experimental::filesystem::directory_iterator(path)) {
        cout << entry.path() << endl;
    }

}

int main() {

    path_to_main_dir();
    string dateread;
    printf("Which file do you want to open? ");
    cout << "---------------------------------------------------------------------------------------------------------" << endl;
    path_to_main_dir();
    cout << endl;
    cout << "---------------------------------------------------------------------------------------------------------" << endl;
    cout << "User: ";
    getline(cin, dateread);
    string path_to_file = "C:/Randomizer/" + dateread + ".txt";
    ifstream readfile(path_to_file.c_str());
    vector<string> words;
    string word;
    while (getline(readfile, word))
    {
        words.push_back(word);
    }
    readfile.close();
    srand(time(NULL));

    string randomword;
    vector<string> rw = { words };
    int num_elements = size(words);
    cout << endl;
    cout << "Number of words in the file: ";
    cout << num_elements;
    cout << endl;
    for (unsigned int a = 0; a < num_elements; a = a + 1)
    {
        randomword = rw[rand() % num_elements];
        cout << randomword << endl;
        rw.erase(remove(rw.begin(), rw.end(), randomword), rw.end());
        num_elements -= 1;
        system("pause");
    }

    goto firstline;

    return 0;
}

Answer 1

If the error only happens in the case where there are duplicates, it could be because the num_elements is wrong. The remove / erase call will have deleted as many duplicates as there are, but num_elements has only been reduced by one.

Fortunatly, vectors know their own size, so rather than trying to remember its internal information for it, you can just ask!

int main()
{
    //...
    //Code to read words from file
    //...

    cout << "Number of words in file: " << words.size() << endl;

    while(!words.empty())
    {
        string randomWord = words[rand() % words.size()];
        cout << randomWord << endl;
        words.erase(remove(words.begin(), words.end(), randomWord), words.end());
    }

    return 0;
}

From what I can see, you only use words to create rw , so we could just use words directly instead.