C ++：如何从.txt文件的一行中读取每行中变量数量未知的行？

Question

I'm working on a project where I need to create a Linked List from a given data file. It contains operation codes, first names, last names, addresses, cities, states, and zip codes. The problem is that there is an unknown number of spaces on the lines that contain an address and the city. An example of the data file is as follows:

A
Donald
Duck
1123 Appleberry Circle
Saint Cloud
MN
88084
A
Barry
Briches
112 New York Ave
Saint Cottleville
FL
78098

I've tried using a combination of:

infile >> FirstName >> LastName;
infile.getline(Address, 20);
infile.getline(City, 20);
infile >> State >> ZipCode;

but when I go to print it out, the output comes out really weird. Any help on the issue would be greatly appreciated. All code I have done is attached.

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <string.h>
#include "list.h"

using namespace std;

int main()
{
    ifstream infile("data2.txt", ios::in);
    ofstream outfile("output2.txt", ios::out);

    char opCode, fname[12], lname[12], address[20], city[12], state[4], 
    zip[6];

    MailListClass mailingList;

    infile >> ws >> opCode;

    while (opCode != 'Q')
    {
        switch (opCode)
        {
            case 'A' :  infile >> fname >> lname;
                        infile.getline(address, 20, '\n');
                        infile >> city >> state >> zip;
                        mailingList.addRecord(fname, lname, address, city, 
                        state, zip, outfile);
                        break;
            case 'P' :  mailingList.printRecord(outfile);
                        break;
        }
        infile >> ws >> opCode;
    }
    return 0;
}

The .h and .cpp struct/class files:

#ifndef LIST_H
#define LIST_H

#include <fstream>

using namespace std;

struct node
{
    char lname[12], fname[12], city[12], address[20], state[4], zip[6];
    node *next;
};

class MailListClass
{
    private:
        node *headPtr, *currPtr, *prevPtr;
    public:
        MailListClass();
        void addRecord(char fname[12], char lname[12], char address[20],
                            char city [12], char state[4], char zip[6],
                            ofstream &outfile);
        void printRecord(ofstream &outfile);
};

#endif 

list.cpp

#include <cstdlib>
#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>

#include "list.h"

using namespace std;

MailListClass::MailListClass()
{
    headPtr = NULL;
    currPtr = NULL;
    prevPtr = NULL;
}

void MailListClass::addRecord(char fname[12], char lname[12], char address[20], char city[12],
                            char state[4], char zip[6], ofstream &outfile)
{
    node *tail = new node;
    tail->next = NULL;
    strcpy(tail->fname, fname);
    strcpy(tail->lname, lname);
    strcpy(tail->address, address);
    strcpy(tail->city, city);
    strcpy(tail->state, state);
    strcpy(tail->zip, zip);

    if (headPtr != NULL)
    {
        currPtr = headPtr;
        while (currPtr->next != NULL)
        {
            currPtr = currPtr->next;
        }
        currPtr->next = tail;
    }
    else
    {
        headPtr = tail;
    }
} 
void MailListClass::printRecord(ofstream &outfile)
{
    currPtr = headPtr;
    while (currPtr != NULL)
    {
        outfile << left << setw(12) << currPtr->lname;
        outfile << setw(12) << currPtr->fname;
        outfile << setw(20) << currPtr->address;
        outfile << setw(12) << currPtr->city;
        outfile << setw(6) << currPtr->state;
        outfile << setw(10) << currPtr->zip << endl;
        currPtr = currPtr->next;
    }
}

The outfile should looks like this:

Last Name    First Name    Address              City   State  Zip
Last Name    First Name    Address              City   State  Zip

but with the getline() in my code, my output looks closer to this:

Last Name    First Name
                  Address#        AddressNameCityCity
Last Name    First Name
                  Address#        AddressName

Answer 1

I'm afraid that questions like this have asked very often. However, here my answer:

I believe, this is the mis-concept:

infile >> FirstName >> LastName;
infile.getline(Address, 20);

It reads FirstName and LastName but the question is where are the line-ends read?

A simplified sample to illustrate this:

#include <iostream>
#include <string>

int main()
{
  std::string name1, name2;
  std::cin >> name1 >> name2;
  std::cout << "name1: '" << name1 << "', name2: '" << name2 << "'\n";
  for (std::string line; std::getline(std::cin, line);) {
    std::cout << "next: '" << line << "'\n";
  }
  return 0;
}

Tested on coliru with

Donald
Duck
1123 Appleberry Circle

given as input (by echo -e ):

$ g++ -std=c++17 main.cpp && echo -e "Donald\nDuck\n1123 Appleberry Circle\n" | ./a.out
name1: 'Donald', name2: 'Duck'
next: ''
next: '1123 Appleberry Circle'
next: ''

Live Demo on coliru

The line read and printed after Duck is empty. This is because the operator<<(std::istream&, std::string&) doesn't read the white space (eg space, tab, line-end) delimiting the text. Hence, the line-ends after Donald and Duck are left in input buffer. After first string input ( Donald >> name1 ), it doesn't hurt. The next input ( Duck >> name2 ) consumes/skips white spaces until a non-whitespace follows. After second input, the line-end stays in input buffer until the next call of std::getline() consumes it.

There are various ways to fix this:

1. Read everything with std::getline() (and, may be, use std::istringstream with input operators to process the read line buffer further).

2. Place a std::getline() after infile >> FirstName >> LastName; to skip rest of line.

3. Use std::istream::ignore() which

   Extracts and discards characters from the input stream until and including delim.

The above sample fixed with std::istream::ignore() :

#include <iostream>
#include <string>

int main()
{
  std::string name1, name2;
  std::cin >> name1 >> name2;
  std::cin.ignore();
  std::cout << "name1: '" << name1 << "', name2: '" << name2 << "'\n";
  for (std::string line; std::getline(std::cin, line);) {
    std::cout << "next: '" << line << "'\n";
  }
  return 0;
}

Tested on coliru again:

$ g++ -std=c++17 main.cpp && echo -e "Donald\nDuck\n1123 Appleberry Circle\n" | ./a.out
name1: 'Donald', name2: 'Duck'
next: '1123 Appleberry Circle'
next: ''

Live Demo on coliru

---

Concerning the "asked very often", here some other questions:

• Why does std::getline() skip input after a formatted extraction?
• cin and getline skipping input
• Issue with cin when spaces are inputted, using string class

There are probably much more. I found the above by
google site:stackoverflow.com c++ input missing