Problems with getline

This is a discussion on Problems with getline within the C++ Programming forums, part of the General Programming Boards category; I have a problem using getline in a loop. The first time that I have to enter a Address, it ...

  1. #1
    Village id10t
    Join Date
    May 2008
    Posts
    57

    Problems with getline

    I have a problem using getline in a loop. The first time that I have to enter a Address, it works. but from there on it just skips the cin for the rest of the gardens..

    Code:
    void inputInformation(GardenInfo gardensP[])
    {
    for(int i=0;i<NR_OF_GARDENS;i++)
    {
      cout<<"Please enter the address of garden "<<i+1<<":"<<endl;
      getline(cin,gardensP[i].Address,'\n');
      cout<<"Please enter the weekday that we will work at garden "<<i+1<<":"<<endl;
      getline(cin,gardensP[i].Day,'\n');
      cout<<"Please enter the number of workers for garden "<<i+1<<":"<<endl;
      cin>>gardensP[i].Workers;
      do{
      cout<<"Please indicate of the garden has a pool"<<endl;
      cin>>gardensP[i].Pool;
      }while (gardensP[i].Pool!='Y' && gardensP[i].Pool!='N');
    }  
    }
    Output looks something like this:

    Please enter the address of garden 1:
    Long Street 12
    Please enter the weekday that we will work at garden 1:
    Monday
    Please enter the number of workers for garden 1:
    4
    Please indicate of the garden has a pool
    Y
    Please enter the address of garden 2:
    Please enter the weekday that we will work at garden 2:
    Monday
    Please enter the number of workers for garden 2:
    6
    Please indicate of the garden has a pool
    N
    Please enter the address of garden 3:
    Please enter the weekday that we will work at garden 3:

    It just skips the Address question after the first one... What am i doing wrong?

    Thanks in advance

  2. #2
    Deathray Engineer MacGyver's Avatar
    Join Date
    Mar 2007
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    3,211
    I could be wrong, but I think you need a cin.ignore() after you get the Y/N for a pool.

  3. #3
    Village id10t
    Join Date
    May 2008
    Posts
    57
    Thanks for the reply MacGyver, but that did not solve the problem... any other idea?

  4. #4
    Deathray Engineer MacGyver's Avatar
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    Mar 2007
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    It probably didn't solve the problem because you didn't do it, or at least didn't do it properly.

    Case in point:

    Code:
    #include <iostream>
    
    int main()
    {
    	std::string s1, s2;
    	int num;
    	char yn;
    	
    	for(int i=0;i<3;i++)
    	{
    		std::cout << "Enter string 1: ";
    		getline(std::cin, s1, '\n');
    		std::cout << "Enter string 2: ";
    		getline(std::cin, s2, '\n');
    		std::cout << "Enter int 1: ";
    		std::cin >> num;
    		do
    		{
    			std::cout << "Enter [Y/N]: ";
    			std::cin >> yn;
    			std::cin.ignore();  /* Important */
    		}
    		while((yn != 'Y') && (yn != 'N'));
    	}
    	
    	return 0;
    }
    First iteration of output without the std::cin.ignore():

    Enter string 1: s1
    Enter string 2: s2
    Enter int 1: 1
    Enter [Y/N]: Y
    Enter string 1: Enter string 2: S2
    First iteration of output with the std::cin.ignore():

    Enter string 1: s1
    Enter string 2: s2
    Enter int 1: 1
    Enter [Y/N]: Y
    Enter string 1: S1

  5. #5
    Village id10t
    Join Date
    May 2008
    Posts
    57
    Ok so i have to put cin.ignore() in before the while to test the input of pool... It works now, but im dont quiet understand why... why is cin.ignore() so important?

  6. #6
    Deathray Engineer MacGyver's Avatar
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    3,211
    Because when you use std::cin to read a char, it reads a char and leaves the '\n' you entered in the stream. Then when getline() is called, it reads until it hits the '\n', which it does right away.

    Example:

    Code:
    cout<<"Please indicate of the garden has a pool"<<endl;
    cin>>gardensP[i].Pool;
    When this happens, and you type "Y" and press enter, this is the input stream:

    Code:
    'Y', '\n'
    std::cin will read the 'Y' char. So the input stream now looks like this:

    Code:
    '\n'
    You then come back to this in the loop:

    Code:
    cout<<"Please enter the address of garden "<<i+1<<":"<<endl;
    getline(cin,gardensP[i].Address,'\n');
    And getline() reads the '\n' in the stream and decides it reached the end of what you wanted.

    Placing std::cin.ignore() after reading the 'Y' char will read and discard the '\n' char.

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