Vector display iterator ends prematurely [duplicate] - c++

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sizeof() a vector
(6 answers)
Closed 2 years ago.
I'm currently working on a final project for one of my introductory classes in college, and I can't seem to find out why my output is cutting out prematurely. I'm trying to append the lines of a text file in the same directory into a vector and randomly select from the vector to get a name for an enemy in a text-based fighting game, but during testing it seems like the vector either only contains three items or the last for loop (the one before the comment blocks, I'm working on it in chunks) only displays three of the possible names. Here's the code:
#include <iostream>
#include <fstream>
#include <ctime>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <vector>
#include <unordered_map>
#include <ctype.h>
using namespace std;
int main() {
srand(time(0));
int userInput;
int player_health = 100;
int boss_health = 200;
int boss_index = rand() % 3;
ifstream boss_list;
string boss_name = "";
string boss_inputs[3] = {"MACHINE GUN", "BOMB ATTACK", "CANE SMACK"};
string user_inputs[3] = {"SWORD ATTACK", "BOMB ATTACK", "MAGIC ATTACK"};
vector<string> boss_list_holder = {};
unordered_map<string, int> attacks = {
{"SWORD ATTACK", rand() % 100},
{"BOMB ATTACK", rand() % 100},
{"MAGIC ATTACK", rand() % 100}
};
unordered_map<string, int> boss_attacks = {
{"MACHINE GUN", rand() % 75},
{"BOMB ATTACK", rand() % 80},
{"CANE SMACK", rand() % 50}
};
boss_list.open("names.txt", ios::in);
while(getline(boss_list, boss_name)) {
//cout << boss_name << endl;
boss_list_holder.push_back(boss_name);
}
for(int j=0; j<(sizeof(boss_list_holder)/sizeof(boss_list_holder[0])); j++) {
cout << boss_list_holder[j] << endl;
}
//cout << "BOSS FIGHT SIMULATOR\n\n";
/*
while(userInput > 3 || userInput < 1) {
cout << "Enter the attack you want to use!\n";
for(int i=0; i<sizeof(user_inputs)/sizeof(user_inputs[0]); i++) {
cout << i + 1 << ". " << user_inputs[i] << " ";
}
cout << "\n";
cin >> userInput;
};
*/
/*
cout << boss_inputs[boss_index] << " ";
cout << boss_attacks[boss_inputs[boss_index]];
*/
return 0;
}
Any and all help would be appreciated. Thank you!

Answer 1

sizeof(boss_list_holder)/sizeof(boss_list_holder[0])
This is a very old-fashioned way of deducing the length of an array, and indeed it only works for arrays.
It doesn't even work on pointers, which people often have instead of arrays without realising it, so std::size(boss_list_holder) is a better general solution.
In your case, simply boss_list_holder.size() is your best bet.
You should also be using unsigned int (or, ideally, std::size_t) for array or vector indices, and your compiler will warn you about unsafe signed/unsigned comparisons if you stick with int.
(Some people will go further and recommend std::vector<string>::size_type, though personally I think that's overkill.)

Answer 2

Your for loop over the boss_list_holder vector is wrong:
for(int j=0; j<(sizeof(boss_list_holder)/sizeof(boss_list_holder[0])); j++)
This sizeof trick only works for fixed-sized arrays (like your user_input), where the elements are stored directly in the allocated memory of the array itself.
This does not work for dynamic containers like std::vector, which boss_list_holder is an instance of. The elements of a std::vector are not stored in the allocated memory of the std::vector object itself (ie, sizeof(boss_list_holder) is not equal to sizeof(string) * NumberOfStrings). They are stored in an array that is allocated elsewhere in memory, and the std::vector object simply holds a pointer to that array (amonst other things).
You need to use the vector's size() method instead, that will return the number of elements that have been put into the std::vector's inner array:
for(size_t j = 0; j < boss_list_holder.size(); ++j)