Redirecting the Input in C programming

We can also redirect input to a program so that, instead of reading a character from the keyboard, a program reads it from a file. Let us now see how this can be done.

To redirect the input, we need to have a file containing something to be displayed. Suppose we use a file called NEWPOEM.TXT containing the following lines

Let's start at the very beginning,

A very good place to start!

We’ll assume that using some text editor these lines have been placed in the file NEWPOEM.TXT. Now, we use the input redirection operator ‘<’ before the file, as shown below:

C>UTIL.EXE < NEWPOEM.TXT

Let's start at the very beginning,

A very good place to start!

C>

The lines are printed on the screen with no further effort on our part. Using redirection we’ve made our program UTIL.C perform the work of the TYPE command.

Both Ways at Once

Redirection of input and output can be used together; the input for a program can come from a file via redirection, at the same time its output can be redirected to a file. Such a program is called a filter. The following command demonstrates this process.

C>UTIL < NEWPOEM.TXT > POETRY.TXT

In this case our program receives the redirected input from the file NEWPOEM.TXT and instead of sending the output to the screen it would redirect it to the file POETRY.TXT.

Similarly to send the contents of the file NEWPOEM.TXT to the printer we can use the following command:

C>UTIL < NEWPOEM.TXT > PRN

While using such multiple redirections don’t try to send output to the same file from which you are receiving input. This is because