Mixing formatted input extractors with getline causes cout display to stick together

问题

The following code seves to establish a movie database and query through it. It works as intended except for the first cout statements being clumped together. The code is as follows.

// array of structures
#include <iostream>
#include <string>
#include <sstream>
#include <stdio.h>
#include <cctype>
using namespace std;

#define NUM_MOVIES 6
//structure
struct movies_iit{
    string title;
    int year;
} films [NUM_MOVIES];
//global variables
char title [20], y, n;
int year;
string search;
//function 1
void sort_on_title(movies_iit films[], int n)
{
//Local struct variable used to swap records
movies_iit temp;    

for(int i=0; i<n-1; i++)
    {
for(int i=0; i<n-1; i++)
        {
/*If s[i].title is later in alphabet than
s[i+1].title, swap the two records*/
        if(films[i].title>films[i+1].title)
            {
                temp = films[i];
                films[i] = films[i+1];
                films[i+1] = temp;
            }  
        }
    }
}
//end function 1
//function query1 prototype
void query1 (movies_iit movie);
//function query2 prototype
void query2 (movies_iit movie);
//function 2 prototype
void printmovie (movies_iit movie);
//beginning of main
int main ()
{
//login
//username: user
//password: word
string mystr;
int n;
char response;
string pass;
string name;
cout << "enter your username "<<endl;
cin >> name;
cout << "enter your password "<<endl;
cin >> pass;

cout << "\n" << endl;

if (name == "user" && pass == "word")
    cout << "Welcome, user." << endl;
else
{cout << "###" <<  "unrecognized username/password combination" << "\t" << "please try again"     << "###" << endl;
    system("PAUSE");
    return 0;
    }
for (n=0; n<NUM_MOVIES; n++)
{
    cout << "Enter title: ";
    getline (cin,films[n].title);
    cout << "Enter year: ";
    getline (cin,mystr);
    stringstream(mystr) >> films[n].year;
}
//sort records, function 1 call
sort_on_title(films, NUM_MOVIES);
cout << "\nYou have entered these movies:\n";
for (n=0; n<NUM_MOVIES; n++) 
    printmovie (films[n]);  //function 2 call
//Query 1
cout << "Perform an alphabetical search? (y/n)" << endl;
cin >> response;

if (response == 'y')
    {cout << "Please enter title" << endl;
    cin >> title;
    for (n=0; n<NUM_MOVIES; n++)
        {query1 (films[n]);
            response == n;
        }
    }
else if (response == 'n')
    cout << "\n" << endl;
else
    cout << "invalid entry" << endl;
//Query 2
cout << "Perform a chronological search? (y/n)" << endl;
cin >> response;
//greater than
if (response == 'y')
{   cout << "greater than what year?" << endl;
    cin >> year;
    for (n=0; n<NUM_MOVIES; n++)
        {   query2 (films[n]);
        }
}
else if (response == 'n')
    cout << "Thank you, goodbye." << endl;
else
    cout << "invalid entry" << endl;
system("pause");
return 0;
}
//end of  main
//function 2 definition
void printmovie (movies_iit movie)
{
  cout << movie.title;
  cout << " (" << movie.year << ")\n";
}
//function query1 defintion
void query1 (movies_iit movie)
{
  if (movie.title == title)
      {cout << " >> " << movie.title;
  cout << " (" << movie.year << ")\n";}
  else
      {cout << movie.title;
  cout << " (" << movie.year << ")\n";}
}
//function query2 definition
void query2 (movies_iit movie)
{
  if (movie.year >= year)
      {cout << movie.title;
        cout << " (" << movie.year << ")\n";
      }
}

I managed to trace the problem back to the login at the beginning of the code, without the

cout << "enter your username "<<endl;
cin >> name;
cout << "enter your password "<<endl;
cin >> pass;

cout << "\n" << endl;

if (name == "user" && pass == "word")
    cout << "Welcome, user." << endl;
else
{cout << "###" <<  "unrecognized username/password combination" << "\t" << "please try again"     << "###" << endl;
    system("PAUSE");
    return 0;
    }

section, the code works fine. Why is the beginning of my code sticking together, and how can I fix it without omitting the login?

回答1:

cin >> pass stops reading at the whitespace, but it is still there in the buffer. When you call getline it sees the newline waiting in the buffer and returns. You need to empty the buffer before you call getline.

See: http://en.cppreference.com/w/cpp/io/manip/ws

It also looks like you have an error here:

for (n=0; n<NUM_MOVIES; n++)
    {query1 (films[n]);
        response == n;
    }

Should that be response = n? As it stands that statement has no utility.

来源：https://stackoverflow.com/questions/20080255/mixing-formatted-input-extractors-with-getline-causes-cout-display-to-stick-toge

标签

c++

iostream