Kernighan and Ritchie Exercise 5-11 is unclear

Question

Here's Exercise 5-11: Modify the program entab and detab (written as exercises in Chapter 1) to accept a list of tab stops as arguments. Use the default tab settings if there are no arguments.

entab is described as

Replace strings of blanks by minimum # of tabs/blanks to achieve same spacing. A tab should be given preference to let the array of chars store the "tab" as one index rather than multiple spaces.

What is a "tab stop" exactly and how can we accept a list of whatever the tab stops are? I'm confused.

Answer 1

When you hit tab, you travel to the next tab stop. For example, many text editors have the tab stops at all multiples of 8 (8, 16, 24, 32, 40, etc) so if you are in column (say) 11 and hit tab you go to column 16. If you're in column 14 and hit tab you also go to column 16. So a tab is not always worth a fixed amount of spaces, but however many are needed to go to the next tab stop.