CODEWITHSUNDEEP
c++getlinecin
Simplicity
Simplicity

Reputation: 48966

std::cin.getline( ) vs. std::cin

When should std::cin.getline() be used? What does it differ from std::cin?

Upvotes: 45

Views: 80203

Answers (6)

p3hzucn
p3hzucn

Reputation: 1

The use of std::cin >> std::ws skips the whitespace, in particular the newline, and carries on reading where the actual content is entered.

int a;
string s;
cin>>a;
getline(cin>>ws, s)

Upvotes: 0

B0rKII
B0rKII

Reputation: 51

(Very simplefied)My answer is, that std :: cin.getline() can contain spaces, while std :: cin >> can not.

Upvotes: 4

roschach
roschach

Reputation: 9396

As already others have answered (even better) roughly speaking, use getline() to read an entire line (i.e., a string terminating with \n) and cin>>var to read a number compatible with the type of var (integer, float, double etc.) or a single word.

In this answer I want to emphasize a problem that arises when mixing the two methods. When you do:

int a;
string s;
cin>>a;
getline(cin, s)

cin leaves an end of line, \n, character which is then read by getline();. It is possible to overcome this problem by using cin.ignore().

int a;
string s;
cin>>a;
cin.ignore();
getline(cin, s)

Upvotes: 1

MSalters
MSalters

Reputation: 180155

Let's take std::cin.getline() apart. First, there's std::. This is the namespace in which the standard library lives. It has hundreds of types, functions and objects.

std::cin is such an object. It's the standard character input object, defined in <iostream>. It has some methods of its own, but you can also use it with many free functions. Most of these methods and functions are ways to get one or more characters from the standard input.

Finally, .getline() is one such method of std::cin (and other similar objects). You tell it how many characters it should get from the object on its left side (std::cin here), and where to put those characters. The precise number of characters can vary: .getline() will stop in three cases: 1. The end of a line is reached 2. There are no characters left in the input (doesn't happen normally on std::cin as you can keep typing) 3. The maximum number of characters is read.

There are other methods and functions that can be used with the std::cin object, e.g.

  std::string s;
  int i;
  std::cin >> s; // Read a single word from std::cin
  std::cin >> i; // Read a single number from std::cin
  std::getline(std::cin, s); // Read an entire line (up to \n) from std::cin
  std::cin.ignore(100); // Ignore the next 100 characters of std::cin

Upvotes: 49

alvelcom
alvelcom

Reputation: 408

In case with char*, std::cin.getline getting line, instead of std::cin getting first word.

Upvotes: 26

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272687

Did you read any documentation (e.g. http://www.cplusplus.com/reference/string/getline/)?

Basically, std::cin (or more generally, any std::istream) is used directly in order to obtain formatted input, e.g. int x; std::cin >> x;. std::cin.getline() is used simply to fill a raw char * buffer.

Upvotes: 9

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