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cin.getline() question

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cin.getline() question

 
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  #1
May 12th, 2009
Well, once again, hello. I'm trying to figure out why when i use 2 cin.getlines after eachother it skips one of them and I cant use it. Take a look if you will:

C++ Syntax (Toggle Plain Text) 
  1. void Join() 
  2. {
  3. char* Username = new char[255];
  4. char* Password = new char[255];
  5.  
  6.     ofstream DataBase("DataBase.txt", ios::app);
  7.     cout << "Welcome New Member, Please Enter a New Username and Password:\n\n";
  8.     cout << "Username: ";
  9.     cin.getline(Username, 255);
  10.     DataBase << Username << "\n";
  11.     cout << "\nPassword: ";
  12.      cin.getline(Password, 255);
  13.     DataBase << Password << "\n\n";
  14.     cout << "\nSaved To Database!\n";
  15.     DataBase.close();
  16.  
  17.     delete [] Username;
  18.     delete [] Password;
  19. }

for some reason when I run the program and goto this function it will skip the first cin.getline and only let me type for the cin.getline that gets the Password. It's wierd because I ran a simple program similar to it, and it works fine:

C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. #include <cstdlib>
  3. #include <conio.h>
  4. using namespace std;
  5.  
  6. int main (int argc, char* argv[]) {
  7.     char* string1 = new char[255];
  8.     char* string2 = new char[255];
  9.  
  10.     cout << "String1: ";
  11.     cin.getline(string1, 255);
  12.  
  13.     cout << "String2: ";
  14.     cin.getline(string2, 255);
  15.  
  16.     cout << "\nString1 = " << string1 << endl;
  17.     cout << "String2 = " << string2 << endl;
  18.  
  19.     delete[] string1;
  20.     delete[] string2;
  21.  
  22.     getch();
  23.     return 0;
  24. }

This code doesnt skip any cin.getline()'s for some reason, could it not work in the other one because of the file i/o? Maybe its making it act wierd? Any help is appreciated, thanks in advance.
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Re: cin.getline() question

 
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  #2
May 12th, 2009
Before the call to Join(), is there another function that leaves unread input (such as a trailing newline) in cin ?
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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Re: cin.getline() question

 
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  #3
May 12th, 2009
I don't think so, I just use a switch/case which then calls it and thats all, heres the complete code:

C++ Syntax (Toggle Plain Text) 
  1. #include <cstdlib>
  2. #include <iostream>
  3. #include <fstream>
  4.  
  5. using namespace std;
  6.  
  7. char* Username = new char[255];
  8. char* Password = new char[255];
  9. char* User = new char[255];
  10.  
  11. void Join() 
  12. {
  13.     ofstream DataBase("DataBase.txt", ios::app);
  14.     cout << "Welcome New Member, Please Enter a New Username and Password:\n\n";
  15.     cout << "Username: ";
  16.     cin.getline(Username, 255);
  17.     DataBase << Username << "\n";
  18.     cout << "\nPassword: ";
  19.      cin.getline(Password, 255);
  20.     DataBase << Password << "\n\n";
  21.     cout << "\nSaved To Database!\n";
  22.     DataBase.close();
  23.  
  24.     delete [] Username;
  25.     delete [] Password;
  26. }
  27.  
  28. void Login() {
  29.  
  30.      ifstream DataBase("DataBase.txt");
  31.      cout << "Welcome Member, Please Enter Your Username and Password:\n\n";
  32.      cout << "Username: ";
  33.      cin >> User;
  34.      DataBase >> Username;
  35.      if (Username==User) cout << "\nUsername Correct!";
  36.      else cout << "\nUsername Incorrect!";
  37.  
  38.  
  39.  
  40.      delete [] User;
  41.      delete [] Username;
  42.      delete [] Password;
  43.      }
  44.  
  45.      void About() {
  46.           }
  47.  
  48.  
  49. int main(int argc, char *argv[])
  50. {
  51.  
  52.     int option;
  53.  
  54.   cout << "DataBase v1.00 BETA!\n\n";
  55.   cout << "1.Login\n";
  56.   cout << "2.Sign-Up\n";
  57.   cout << "3.About\n";
  58.   cout << "4.Exit\n\n";
  59.   cout << "Option(1-4): ";
  60.   cin >> option;
  61.  
  62.   switch (option) {
  63.          case 1:
  64.               Login();
  65.               break;
  66.          case 2:
  67.               Join();
  68.               break;
  69.          case 3:
  70.               About();
  71.               break;
  72.          case 4:
  73.               break;
  74.          default:
  75.                  cout << "Not An Option!";
  76.                  break;
  77.                  }
  78.  
  79.  
  80.     system("PAUSE");
  81.     return EXIT_SUCCESS;
  82. }

Thanks for replying.
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Re: cin.getline() question

 
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  #4
May 13th, 2009
How about in you use Login() where you use cin instead of getline?
C++ Syntax (Toggle Plain Text) 
  1. cin >> User;
Last edited by Dave Sinkula; May 13th, 2009 at 12:11 am.
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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Re: cin.getline() question

 
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  #5
May 13th, 2009
You'll have to use cin.ignore() to clean the input buffer, read this thread
"Never argue with idiots, they just drag you down to their level and then beat you with experience."
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Re: cin.getline() question

 
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  #6
May 13th, 2009
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Originally Posted by Deme View Post
I don't think so, I just use a switch/case which then calls it and thats all, heres the complete code:

C++ Syntax (Toggle Plain Text) 
  1. #include <cstdlib>
  2. #include <iostream>
  3. #include <fstream>
  4.  
  5. using namespace std;
  6.  
  7. char* Username = new char[255];
  8. char* Password = new char[255];
  9. char* User = new char[255];
  10.  
  11. void Join() 
  12. {
  13.     ofstream DataBase("DataBase.txt", ios::app);
  14.     cout << "Welcome New Member, Please Enter a New Username and Password:\n\n";
  15.     cout << "Username: ";
  16.     cin.getline(Username, 255);
  17.     DataBase << Username << "\n";
  18.     cout << "\nPassword: ";
  19.      cin.getline(Password, 255);
  20.     DataBase << Password << "\n\n";
  21.     cout << "\nSaved To Database!\n";
  22.     DataBase.close();
  23.  
  24.     delete [] Username;
  25.     delete [] Password;
  26. }
  27.  
  28. void Login() {
  29.  
  30.      ifstream DataBase("DataBase.txt");
  31.      cout << "Welcome Member, Please Enter Your Username and Password:\n\n";
  32.      cout << "Username: ";
  33.      cin >> User;
  34.      DataBase >> Username;
  35.      if (Username==User) cout << "\nUsername Correct!";
  36.      else cout << "\nUsername Incorrect!";
  37.  
  38.  
  39.  
  40.      delete [] User;
  41.      delete [] Username;
  42.      delete [] Password;
  43.      }
  44.  
  45.      void About() {
  46.           }
  47.  
  48.  
  49. int main(int argc, char *argv[])
  50. {
  51.  
  52.     int option;
  53.  
  54.   cout << "DataBase v1.00 BETA!\n\n";
  55.   cout << "1.Login\n";
  56.   cout << "2.Sign-Up\n";
  57.   cout << "3.About\n";
  58.   cout << "4.Exit\n\n";
  59.   cout << "Option(1-4): ";
  60.   cin >> option;
  61.  
  62.   switch (option) {
  63.          case 1:
  64.               Login();
  65.               break;
  66.          case 2:
  67.               Join();
  68.               break;
  69.          case 3:
  70.               About();
  71.               break;
  72.          case 4:
  73.               break;
  74.          default:
  75.                  cout << "Not An Option!";
  76.                  break;
  77.                  }
  78.  
  79.  
  80.     system("PAUSE");
  81.     return EXIT_SUCCESS;
  82. }

Thanks for replying.
You could be facing the problem at either of these lines :
C++ Syntax (Toggle Plain Text) 
  1.  cin >> User;
C++ Syntax (Toggle Plain Text) 
  1.  cin >> option;

Most probably, they would leave a newline behind, in the input stream. Hence, the first getline() used after cin would just 'eat' that newline, and wont take any input.

You should better keep habit of using cin.ignore() to flush the input stream before using getline ( or even cin; i had faced this problem in that too..tho not so sure )

C++ Syntax (Toggle Plain Text) 
  1. cin.ignore();
  2. cin.getline();

cin.ignore() also has overloaded versions. You should check them out.
Bhoot
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Re: cin.getline() question

 
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  #7
May 13th, 2009
Thanks i'll try cin.ignore(), and by the way, i don't think i'd want to just use cin, because when i do it doesnt allow spaces...
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Re: cin.getline() question

 
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  #8
May 13th, 2009
Thanks guys, it worked like a charm.. ^_^
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