I try to take a random word from a vector but it takes the same words everytime

Question

As I mentioned on the title; I have a vector which stores a bunch of words(around 2000 words) and in a part of the project it's expected from me that take a random word from that vector and display it. (the project is word finding-like) I have two classes that one of is main, and other is for taking word from vector. I attached the codes below. Something must have escaped my notice, but I can't get what it is somehow.

#include <iostream>
#include <vector>//must be
#include <string>//must be
#include "Dictionary.h"
#include <set>
using namespace std;

int main()                               //main
{
   vector<string> words;
   Dictionary dict(words);
   words = dict.setElements();
   string randomWord = dict.getaRandomWord(words);   //this line is for generate a random word
   cout << randomWord;         

   return 0;
}

class Dictionary                        //dictionary class
{
public:

Dictionary(::vector<string> a) {
    //getWordsFromFile() = a;
}


/*  public :vector<string> getWordsFromFile() {
vector<string> words;
ifstream inFile;
string tmp;
inFile.open("words.txt");
while (!inFile.eof()) {
    inFile >> tmp;
    words.push_back(tmp);
}

return words;


}*/

vector<string> setElements() {
// Declaring Vector of String type 
set<string> wordsSet;
string buffer;
vector<string> wordsVector;
ifstream inFile;
string tmp;
inFile.open("words.txt");

while (!inFile.eof()) {
    inFile >> buffer;
    wordsSet.insert(buffer);
}

for (set<string>::iterator it = wordsSet.begin(); it != wordsSet.end(); ++it) {
    wordsVector.push_back(*it);
}


/*for (int i = 0; i < wordsVector.size(); i++) {
    cout << wordsVector.at(i)<<endl;            //its for displaying the elements of the vector
}*/

return wordsVector;


}

string getaRandomWord(vector<string> a) {           //function that has supposed to be generate a random word
    
    vector<string> currentVector = a;
    string randomWord;
    int randomNumber = rand() % currentVector.size();
    randomWord = currentVector.at(randomNumber);
    return randomWord;
}
};

takes aging everytime

EDIT: I placed the seed inside the constructor but leaved other code untouched.So, only changing I made is adding a line of srand(time(nullptr)); inside the Dictionary cons.

class Dictionary
{
public:
Dictionary(::vector<string> a) {
    //getWordsFromFile() = a;
    srand(time(nullptr));
     .
     .
     .
}

And the output was like thumb-trash-truly... There is still an alphabetical order.

Answer 1

In order to get a more random number, you need to give it a value to base random values off of, otherwise it will always give the same value. In order to get different values, you will probably want to seed your random number generator with the time to get a greater distribution. Here is a good explanation of what is going on, or you can check the documentation.
What you want to use is std::srand(std::time(null)); one time at the beginning of the program, generally in the constructor. This gives a different set of pseudorandom numbers that will be generated for every pass of the program.