将数据从文件读取到结构体C ++的数组中 [英] Reading data from file into array of structs C++

问题描述

我有一个示例txt文件，并希望将该文件的内容读入结构数组。
我的persons.txt文件包含5个任意的每行一个。

I have a sample txt file and want to read the contents of the file into an array of structs. My persons.txt file contains 5 arbitrary nos one on each line.

7
6
4
3
2

我的程序如下所示：

#include <iostream>
#include <fstream>

using namespace std;

struct PersonId
{
    typedef PersonId* ptr;
    PersonId();
    int fId;
}; 

istream& operator >> (istream& is, PersonId &p)
{
    is >> p;
    // return is;
    // return p.read(is);
}

// istream& PersonData::read(std::istream& is) 
// {
//  is >> fId;
//  return is;
// }


int main ()
{
    ifstream indata;
    int i, is;
    indata.open("persons.txt", ios::in); // opens the file

    if(!indata) 
    { // file couldn't be opened
          cout << "Error: file could not be opened" << endl;
          exit(1);
    }

    int n = 5;
    PersonId* p;
    p = (PersonId*) malloc (n * sizeof(PersonId));

    while ( !indata.eof() )
    { // keep reading until end-of-file
    	// p[i].read();
    	indata >> is;
    	i++;
    	cout << "The next number is "<< is << endl;
            cout << "PersonId [" << i << "] is " << p[i].fId << endl;
        // indata >> is; // sets EOF flag if no value found
    }
    return 0;
}

我的输出如下所示：

test6.cpp: In function ‘std::istream& operator>>(std::istream&, PersonId&)’:
test6.cpp:27: warning: control reaches end of non-void function
The next number is 7
PersonId [1] is 0
The next number is 6
PersonId [2] is 0
The next number is 4
PersonId [3] is 0
The next number is 3
PersonId [4] is 0
The next number is 2
PersonId [5] is 0

推荐答案

istream& operator >> (istream& is, PersonId &p)
{
    is >> p.fId;
    return is;
}

（读取p的成员fId，而不是整个结构）

(Reading the member fId of p, not the entire structure)

而在main中，读取结构，而不是值：

And the the while in main, read the structure, not a value:

而不是

indata >> is;

put

indata >> p[i];

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