Standard Input and Output Streams

What are standard input and output streams? #

So far, the output of our programs has been displayed on the console. Although the console is often the ultimate target of output, this is not always the case. The objects that can accept the output of a program are called standard output streams. Similarly, the standard input stream comes into play when some input is taken from the user and used by the program.

Character stream #

The standard output stream is character-based; everything displayed is first converted to the corresponding character representation and sent to the output as characters.

Example #

The integer value 100 is not sent to the output as the value 100, but it is sent as three characters ‘1’, ‘0’, and ‘0’.

Similarly, the keyboard can be thought of as the standard input stream of a program, and it is also character-based. The information always comes as characters to be converted to data. For example, the integer value 42 actually comes through the standard input as the characters 4 and 2. These conversions happen automatically.

This concept of consecutive characters is called a character stream. As D’s standard input and standard output fit this description, they are character streams.

Standard input and output streams in D #

The names of the standard input and output streams in D are stdin and stdout, respectively.

Operations on these streams normally require the name of the stream, a dot operator and the operation, as in stream.operation(). Because stdin's reading methods and stdout's writing methods are used very commonly, these operations can be called without the need of the stream name and the dot operator.

For example, writeln, which we’ve been using in the previous chapters, is actually short for stdout.writeln. Similarly, write is short for stdout.write. Accordingly, the “Hello World” program can also be written as follows: