C++ pass empty vector of structs to a function

Question

I am trying to pass an empty vector of structures to a function which will read from a file and it will return the number of records read -- it will be an integer.

I initialize the vector of structures in main and when I attempt to pass it to the function as I would regularly do it:

int read_records(vector<player> player_info)

It gives me a "player is undefined" error. I have found a way to go around it as you will see in my code below but logic leads me to believe that there should be a way to pass the empty vector without having to fill in the first subscript.

The code is below. Please note that the read function is not yet complete as I am still wondering about the vector of structs.

#include <iostream>
#include <vector>
#include <string>
#include <cstdlib>
#include <fstream>
using namespace std;

//function prototypes
int read_records(struct player* player_info);

/*
* Define a struct called player that will consist
* of the variables that are needed to read in each
* record for the players. 2 strings for the first
* and last names and 1 integer to hold the statistics
*/
struct player
{
    string first;
    string last;
    int stats;
};

int main(void)
{
    int sort_by, records_read;

    vector<player> player_info(1);
    player * point = &player_info[0];


    cout << "Welcome to Baseball player statistics program!" << endl;
    cout << "How should the information be sorted?" << endl;
    cout << "Enter 1 for First Name" << endl;
    cout << "Enter 2 for Last Name" << endl;
    cout << "Enter 3 for Points" << endl;
    cout << "Enter your selection: ";
    cin >> sort_by;

    //read the records into the array
    records_read = read_records(point);


    system("Pause");

    return 0;
}
int read_records(struct player* player_info)
{
    //declare the inputstream
    ifstream inputfile;

    //open the file
    inputfile.open("points.txt");

    //handle problem if the file fails to open for reading
    if (inputfile.fail())
    {
        cout << "The player file has failed to open!" << endl;
        exit(EXIT_FAILURE);
    }
    else
    {
        cout << "The player file has been read successfully!" << endl;
    }

    return 5;

}

Answer 1

Define the type player before you attempt to declare functions that need to know about that type.

struct player
{
    string first;
    string last;
    int stats;
};

int read_records(vector<player> player_info);

Your workaround was successful because naming player in struct player* acts as a [forward] declaration, in a way that naming it in vector<player> does not. (The whys and wherefores of this are too broad for this answer and are covered elsewhere on SO and in your C++ book.)

As an aside, I doubt you want to take that vector by value.

Answer 2

为什么不在int read_records(vector<player> player_info)之前放置struct player定义。