C Primer Plus®, Third Edition

Buffers

When you run the previous program on some systems, the text you input is echoed immediately. That is, a sample run would look like this:

HHeelllloo,,  tthheerree..  II  wwoouulldd[enter]
lliikkee  aa  #

The preceding behavior is the exception. On most systems, nothing happens until you press Enter, as in the first example. The immediate echoing of input characters is an instance of unbuffered (or direct) input, meaning that the character you type is immediately made available to the waiting program. The delayed echoing, on the other hand, illustrates buffered input, in which the characters you type are collected and stored in an area of temporary storage called a buffer. Pressing Enter causes the block of characters (or single character, ...