Cin.Getline() Can Run Into Problems

C++ Programming Tricks

std::cin.getline() can run into problems when used with std::cin >> var:

getline can be provided a third argument--a "stop" character. This character ends getline's input. The character is eaten and the string is terminated. Example:

 std::cin.getline(str, 100, '|')
 

If std::cin.getline() is not provided a "stop" character as a third argument, it will stop when it reaches a newline.

 Given: 
 
   float fl;
   std::cin >> fl;
   char str[101]
   std::cin.getline(str, 101);
 And you type: 3.14
 

3.14 is read into fl . The newline following the 3.14 is still sitting on the input buffer. std::cin.getline(str, 101) immediately processes the newline that is still on the input buffer. str becomes an empty string. The illusion is that the application "skipped" the std::cin.getline() statement.

The solution is to add std::cin.ignore(); immediately after the first std::cin statement. This will grab a character off of the input buffer (in this case, newline) and discard it.

 std::cin.ignore() can be called three different ways: 
 No arguments: A single character is taken from the input buffer and discarded:
 
 std::cin.ignore(); //discard 1 character 
 One argument: The number of characters specified are taken from the input 
 buffer and discarded:
 
 std::cin.ignore(33); //discard 33 characters 
 Two arguments: discard the number of characters specified, or discard 
 characters up to and including the specified delimiter (whichever comes first):
 
 std::cin.ignore(26, '\n'); //ignore 26 characters or to a newline, 
 whichever comes first