Presented at FSE 2015

1. An Empirical Study of Goto in C
Code from GitHub Repositories
Mei Nagappan, Romain Robbes, Yasutaka Kamei, Éric
Tanter, Shane McIntosh, Audris Mockus, Ahmed E. Hassan

2. Go-to statement
considered
harmful (1968)

3. A Case against the
GO TO Statement
(1968)

4. Do Practitioners care?

5. Do Practitioners care?
https://xkcd.com/292/

6. Do Practitioners care?

7. Do Practitioners care?

8. Do Practitioners care?

9. Impact of Article on Research Community

10. Impact of Article on Research Community

11. Impact of Article on Research Community

12. Impact of Article

13. Koenig: Dijkstra provides strong logical evidence for why
goto statements can introduce problems in software.

14. Well informed and often well argued
opinions

15. Shift from opinion to facts

16. Our Goal: Empirically Examine the use of
goto
Shift from opinion to facts

17. Example
Label
Goto Statement

18. PRELIMINARY ANALYSIS
Do developers use goto
statements in their source code?

19. Experiment
11,627
Projects
Goto Miner

20. 11,627
Projects
Goto Miner
3,093
Projects
Despite the popularity of Dijkstra’s
case against goto…

21. 11,627
Projects
Goto Miner
3,093
Projects
246,657 out of the 2,150,387 files
(11.47%)
Extent of use of goto statements by
Developers is non-trivial

22. Two Research Questions

23. Two Research Questions
RQ1: What are goto statements used
for?

24. Two Research Questions
RQ1: What are goto statements used
for?
RQ2: Do developers remove/modify
goto statements?

25. Qualitative Analysis
246,669
C files
384
files
Properties
and
Purposes
of Goto
Iterative
Tagging
Sample
Selection

26. Basic Bean Counting

27. Num of Goto Statements
per Function
Num of Goto Labels
per Function
Not many goto statements per function

28. Num of Goto Statements
per Function
Num of Goto Labels
per Function
Not many goto statements per function
Very few lines of code in label blocks
Median = 4 LOC

29. Properties

30. Context
Why did Dijkstra think goto statements
would have ‘disastrous effects’?
‘The go to statement as it stands is just
too primitive; it is too much an invitation
to make a mess of one’s program.’

31. Desire to make programs verifiable

32. Desire to make programs verifiable

33. 3 ways to reach the code under the label
“back”

34. First way: Top down execution

35. Second way: condition2 == true

36. Third way: done == false

37. Difficult to know what has been
executed so far.
Hence go to statements must be
avoided!

38. Our Findings

39. Multiple goto jumps to the same label
This is what Dijkstra feared about!
62%

40. Single point of entry into label block!
9%
But not all use of goto is like what
Dijkstra feared!

41. Stacking labels at the bottom of
functions is prevalent
27%

42. Spaghetti code is uncommon
6%

43. Most of the jumps are forward, not
backwards
90%
14%

44. Purposes

45. Most goto usage is for error handling
and cleanup
Error Handling =
80%
Cleanup = 40%

46. Most goto usage is for error handling
and cleanup
Error Handling =
80%
Goto and labels used to emulate a try/catch or
finally mechanism
Cleanup = 40%

47. Less intuitive usages such as control-
exit and loop-create are less common
10%

48. Less intuitive usages such as control-
exit and loop-create are less common
9%
Most usages of goto statements appear to
be for error handling and cleanup

49. Quantitative Analysis
Mine
Commits
6 OSS
Projects

50. Quantitative Analysis
Mine
Commits
6 OSS
Projects
Link to
Bugs
180 Days
Of Commit
History

51. Quantitative Analysis
Mine
Commits
6 OSS
Projects
Link to
Bugs
180 Days
Of Commit
History
Bug Fix
Commits
Extract
Goto

52. Almost no Gotos are removed/modified
in the post-release phase of a project
0
2
4
6
8
10
12
14
16
Removed
Modified

53. Even fewer Gotos are
removed/modified in the post-release
bug fixes
0
1
2
3
4
5
6
Removed
Modified

54. Even fewer Gotos are
removed/modified in the post-release
bug fixes
0
1
2
3
4
5
6
Removed
Modified
Developers did not remove/modify goto
statements in the post-release phase.

55. Summary