如何将文本文件读入指针数组？ （C ++）

Question

What I need to do is read a text file into an array. Each line has four parts; first name, the ID, the height, and the weight. There are 13 lines in the text file, so I need to do it 13 times. I'm going to write a loop to make it work (and will be in a function I will parse the array to.) I know how to do it with a basic array, but we're supposed to use structs for this. I've looked around to try to find out how to do this, but nothing's really working for me. Here's the code I have so far.

#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;
struct person
{
string firstname;
int id;
double height;
double weight;
};
int main()
{
person array[13];
person *ptr;
ptr = &array[0];
ifstream inData;
inData.open("peeps.txt");
while(!inData.eof())
{
    for(ptr = &array[0]; ptr < &array[13];ptr++)
    {
        inData >> person[ptr].firstname >> person[ptr].id
        >> person[ptr].height >> person[ptr].weight;


    }
}
}

Answer 1

The way you're doing it is fairly messy, but it's almost correct. Inside the for loop, you're trying to index person , which is a class. That doesn't make much sense. Instead, you have ptr which is pointing to each of the person objects in the array at each iteration, so you can just dereference it and assign to its members:

inData >> ptr->firstname >> ptr->id
>> ptr->height >> ptr->weight;

However, even worse, you have undefined behaviour in the for loop when you do array[13] . There is no element at index 13 so you can't attempt to access it like this. You could change the condition to ptr <= &array[12] , but still, this is very messy.

To be clear though, you definitely don't have an array of pointers as you have said. Instead, you have an array of person s.

ptr = &array[0];

This takes the address of the first person in the array and assigns it to pointer. You can do this much more easily by taking advantage of array-to-pointer conversion:

ptr = array;

Also, eof() as your while criteria is often not a very good idea. It doesn't give a good indication of whether the next set of reads will succeed.