Create player objects based on the number of players from user input? - c++

Question

Background:
I have created a player class and I want to ask the user how many players are going to play the game? Based on the user input I am trying to create that many instances of the player class. However, I used the following links to help me:
Create object using user input
http://www.cplusplus.com/forum/beginner/197342/
So, I tried their solution:
#include "Player.h"
int main() {
int totalPlayers = -1;
cout << "Enter total number of players: ";
while ((totalPlayers < 1) && (totalPlayers > 5)) {
cout << "How many players will be playing? (1-5): ";
cin >> totalPlayers;
}
vector<Player> players(totalPlayers);
system("pause");
}
I get the error: Unhandled exception at 0x763F40B2 in 16LinearChess.exe: Microsoft C++ exception: std::length_error at memory location 0x003BF690.
So, I googled this exact error and found this link: Error : std::length_error at memory location
So, firstly his code was no-where related to mine, but the error was same. I did not understand the answer, but I thought that I had to create the instances using heap memory. So I tried that:
#include "Player.h"
int main() {
int totalPlayers = -1;
cout << "Enter total number of players: ";
while ((totalPlayers < 1) && (totalPlayers > 5)) {
cout << "How many players will be playing? (1-5): ";
cin >> totalPlayers;
}
vector<Player> *players = new Player(totalPlayers);
delete[] players;
system("pause");
}
I got two errors: Severity Code Description Project File Line Suppression State
Error (active) E0144 a value of type "Player *" cannot be used to initialize an entity of type "std::vector<Player, std::allocator> *" 16LinearChess D:\Keshav\Programming Languages\C++\Beginner\01 Michael Dawson\16LinearChess\LinearChess.cpp 64
Severity Code Description Project File Line Suppression State
Error (active) E0289 no instance of constructor "Player::Player" matches the argument list 16LinearChess D:\Keshav\Programming Languages\C++\Beginner\01 Michael Dawson\16LinearChess\LinearChess.cpp
This is my Player class:
#include <iostream>
class Player : public Board {
protected:
int m_position;
Log logger;
int m_playerNumber;
public:
static int m_numberOfPlayers;
Player() :m_position(0) {
++m_numberOfPlayers;
m_playerNumber = m_numberOfPlayers;
}
void m_SetPlayerPosition(int &position) {
if ((position < 0) || (position > 100)) {
m_position = 0;
logger.Error("Position cannot be less than or greater than 100. Your position has been reset to 0 because you fell out of the map.");
}
else {
m_position = position;
}
m_SetBoardPosition(m_position, m_numberOfPlayers); // update the position on the board.
}
friend ostream &operator << (ostream &os, Player &player) {
os << "Player position on board: " << player.m_position << "\nPlayer Number: " << player.m_playerNumber << '\n';
return os;
}
};
int Player::m_numberOfPlayers = 0; // initializing total number of players.
Thank You!

Answer 1

The problem is with your while loop:
int totalPlayers = -1;
cout << "Enter total number of players: ";
while ((totalPlayers < 1) && (totalPlayers > 5)) {
cout << "How many players will be playing? (1-5): ";
cin >> totalPlayers;
}
The while loop will only run if the condition is true, but the condition can never be true since no number can be smaller than 1, but also greater than 5. And since the condition is not true, the while loop will never run, and totalPlayers will be equal to -1, which is something you never want if you're trying to access an array index.
Change it to this: totalPlayers < 1 || totalPlayers > 5 with an || instead, and you should be fine.
And for the error:
Unhandled exception at 0x763F40B2 in 16LinearChess.exe: Microsoft C++ exception: std::length_error at memory location 0x003BF690.
Your code threw an exception because totalPlayers is equal to -1. So you basically did this:
vector<Player> players(-1);
Which makes no sense since you are creating an array that hold -1 elements? So the code threw an exception telling you that something is wrong. The std::length_error should give a hint about what's wrong.
Also like many of the comments have stated, don't do this:
vector<Player> *players = new Player(totalPlayers);
The whole purpose of a vector is so you don't do that. Your first example works fine:
vector<Player> players(totalPlayers);

Answer 2

std::length_error occurs if std::vector attempts to resize to a size that is above the max_size(). Most often, this happens from a bad input -- such as -1 which will be converted to the largest unsigned value for std::vector<T>::size_type.
Judging by the code you shared, the problem is actually due to your while loop condition:
while ((totalPlayers < 1) && (totalPlayers > 5))
It is not possible for totalPlayers to be both simultaneously less than 1 and greater than 5 -- so this loop is never entered. Since the default value you assign to totalPlayers is -1, the size you resize to overflows and becomes the largest unsigned value -- which triggers the std::length_error.
Fixing this condition should fix your error.