An Empirical Study of Goto in C Code from GitHub Repositories
- 1. An Empirical Study of Goto in C Code from GitHub Repositories Mei Nagappan, Romain Robbes, Yasutaka Kamei, EÌric Tanter, Shane McIntosh, Audris Mockus, Ahmed E. Hassan
- 3. A Case against the GO TO Statement (1968)
- 9. Impact of Article on Research Community
- 10. Impact of Article on Research Community
- 11. Impact of Article on Research Community
- 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
- 18. PRELIMINARY ANALYSIS Do developers use goto statements in their source code?
- 20. 11,627 Projects Goto Miner 3,093 Projects Despite the popularity of Dijkstraâs case against gotoâŠ
- 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
- 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
- 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 âdisastrous effectsâ? âThe go to statement as it stands is just too primitive; it is too much an invitation to make a mess of oneâs program.â
- 31. Desire to make programs verifiable
- 32. Desire to make programs verifiable
- 33. 3 ways to reach the code under the label âbackâ
- 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
- 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