C++ for Scientists - Technische Universität Dresden

2.7. INPUT AND OUTPUT 45
std::ifstream datafile( ”file.dat” ) ;
assert( datafile.is open() );
datafile.close();
return 0;
}
In this example, assert is used to abort the program execution if datafile compares equal to 0,
which happens when the opening of the file was unsuccessful.
2.7 Input and output
C ++ uses a convenient abstraction called streams to perform input and output operations in
sequential media such as the screen or the keyboard. A stream is an object where a program
can either insert characters to or extract from. The standard C ++ library includes the header
file iostream, where the standard input and output stream objects are declared.
2.7.1 Standard Output (cout)
By default, the standard output of a program is the screen, and the C ++ stream object defined
to access it, is cout.
cout is used in conjunction with the insertion operator, which is written as ≪ . It may be used
more than once in a single statement. This is especially useful if we want to print a combination
of variables and constants or more than one variable. Consider this example:
std::cout ≪ ”Hello World, my name is ” ≪ name ≪ std::endl ;
std::cout ≪ ”I am ” ≪ age ≪ ” years old.” ≪ std::endl ;
If we assume the name variable to contain the value Jane and the age variable to contain 25
the output of the previous statement would be:
Hello World, my name is Jane.
I am 25 years old.
The endl manipulator produces a newline character. An alternative representation of endl is the
character ’n’.
2.7.2 Standard Input (cin)
The standard input device is usually the keyboard. Handling the standard input in C ++ is done
by applying the overloaded operator of extraction ≫ on the cin stream. The operator must be
followed by the variable that will store the data that is going to be extracted from the stream.
For example:
int age;
std::cin ≫age;