GOTO still considered harmful? [closed]

Answer 1

Donald E. Knuth answered this question in the book "Literate Programming", 1992 CSLI. On p. 17 there is an essay "Structured Programming with goto Statements" (PDF). I think the article might have been published in other books as well.

The article describes Dijkstra's suggestion and describes the circumstances where this is valid. But he also gives a number of counter examples (problems and algorithms) which cannot be easily reproduced using structured loops only.

The article contains a complete description of the problem, the history, examples and counter examples.

Answer 2

The original paper should be thought of as "Unconditional GOTO Considered Harmful". It was in particular advocating a form of programming based on conditional (if) and iterative (while) constructs, rather than the test-and-jump common to early code. goto is still useful in some languages or circumstances, where no appropriate control structure exists.

Answer 3

You can use it for breaking from a deeply nested loop, but most of the time your code can be refactored to be cleaner without deeply nested loops.

Answer 4

In C, goto only works within the scope of the current function, which tends to localise any potential bugs. setjmp and longjmp are far more dangerous, being non-local, complicated and implementation-dependent. In practice however, they're too obscure and uncommon to cause many problems.

I believe that the danger of goto in C is greatly exaggerated. Remember that the original goto arguments took place back in the days of languages like old-fashioned BASIC, where beginners would write spaghetti code like this:

3420 IF A > 2 THEN GOTO 1430

Here Linus describes an appropriate use of goto: http://www.kernel.org/doc/Documentation/CodingStyle (chapter 7).

Answer 5

Denying the use of the GOTO statement to programmers is like telling a carpenter not to use a hammer as it Might damage the wall while he is hammering in a nail. A real programmer Knows How and When to use a GOTO. I’ve followed behind some of these so-called ‘Structured Programs’ I’ve see such Horrid code just to avoid using a GOTO, that I could shoot the programmer. Ok, In defense of the other side, I’ve seen some real spaghetti code too and again, those programmers should be shot too.

Here is just one small example of code I’ve found.

  YORN = ''
  LOOP
  UNTIL YORN = 'Y' OR YORN = 'N' DO
     CRT 'Is this correct? (Y/N) : ':
     INPUT YORN
  REPEAT
  IF YORN = 'N' THEN
     CRT 'Aborted!'
     STOP
  END

-----------------------OR----------------------

10:  CRT 'Is this Correct (Y)es/(N)o ':

     INPUT YORN

     IF YORN='N' THEN
        CRT 'Aborted!'
        STOP
     ENDIF
     IF YORN<>'Y' THEN GOTO 10

Answer 6

In Linux: Using goto In Kernel Code on Kernel Trap, there's a discussion with Linus Torvalds and a "new guy" about the use of GOTOs in Linux code. There are some very good points there and Linus dressed in that usual arrogance :)

Some passages:

Linus: "No, you've been brainwashed by CS people who thought that Niklaus Wirth actually knew what he was talking about. He didn't. He doesn't have a frigging clue."

-

Linus: "I think goto's are fine, and they are often more readable than large amounts of indentation."

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Linus: "Of course, in stupid languages like Pascal, where labels cannot be descriptive, goto's can be bad."