getline function problem

nostaque · #1 03-Dec-2008, 11:14

Hi guys,

I am stuck at a very simple code. Could you please help me out.

The getline() function works as normal, but inside the if statement the function does not perform.

I tried on dev-c++ and code::block under winxp sp2.

Thanks in advance,

CPP / C++ / C Code:

#include <iostream>
#include <string>
using namespace std;

int main()
{
   string s, line;
   cout <<"enter line: ";
   getline(cin, line);
   cout << line << endl;

   cout <<"1. Add chore to the list. \n";
   cout <<"2. Delete chore from the list. \n";

   int choice;
   cout <<"Enter your choice: ";
   cin >> choice;
   if(choice == 1)
   {
      cout <<"Enter chore: ";
      getline(cin, line);
      cout << line << endl;
   }
   if(choice == 2)
   {
      cout <<"Enter chore to delete: \n";
      getline(cin, line);
      cout << line << endl;
   }
return 0;
}

davekw7x · #2 03-Dec-2008, 11:43

Quote:

Originally Posted by nostaque

...
The getline() function works as normal...

Here's the drill: getline() stops reading when it encounters a newline character in the stream. (It removes the newline from the stream but does not put it into the string.)

When you use ">>" to read a numeric data value into your program, the ">>" converts everything it can from the input stream, and then stops. So, there will always be (at least) a newline character left in the system input buffer. The next time you call getline, it sees the newline and returns with the string empty.

Bottom line: After using ">>" to read a numeric value, you get rid of the rest of that line before calling getline.

For example, in your program:

CPP / C++ / C Code:

    int choice;
    cout << "Enter your choice: ";
    cin >> choice;
    if (!cin) {
        cout << "Invalid entry: Can't convert to integer." << endl;
        exit(EXIT_FAILURE);
    }

    while (cin.get() != '\n') // A do-nothing loop to eat the rest of the line
        ;

    if (choice == 1) {
        cout << "Enter chore: ";
        getline(cin, line); // Starts with a brand new input line
.
.
.

Another way might be to use an extra getline after the ">>" operation:

CPP / C++ / C Code:

    int choice;
    cout << "Enter your choice: ";
    cin >> choice;
    if (!cin) {
        cout << "Invalid entry: Can't convert to integer." << endl;
        exit(EXIT_FAILURE);
    }
    string dummy;
    getline(cin,dummy); // Read the rest of the line and throw it away

    if (choice == 1) {
        cout << "Enter chore: ";
        getline(cin, line);
        cout << line << endl;
    }

Another way, that some prefer, is to use the istream member function ignore()

CPP / C++ / C Code:

    cin >> choice;
    if (!cin) {
        cout << "Invalid entry: Can't convert to integer." << endl;
        exit(EXIT_FAILURE);
    }
    // Eat the rest of the line
    cin.ignore(std::numeric_limits<std::streamsize>::max(),'\n');

    if (choice == 1) {
        cout << "Enter chore: ";
        getline(cin, line);
        cout << line << endl;
    }

Regards,

Dave

nostaque · #3 03-Dec-2008, 15:29

Wow !
That's something you don't see everyday.
Thanks Dave,

WaltP · #4 05-Dec-2008, 01:09

Quote:

Originally Posted by nostaque

Wow !
That's something you don't see everyday.

We do!

.

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getline function problem

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