Common types of computer bugs

Common types of computer bugs

• Conceptual error (code is syntactically correct, but the programmer or designer intended it to do something else)

Arithmetic bugs

• Division by zero
• Arithmetic overflow or underflow
• Loss of arithmetic precision due to rounding or numerically unstable algorithms

Logic bugs

• Infinite loops and infinite recursion
• Off by one error, counting one too many or too few when looping

Syntax bugs

• Use of the wrong operator, such as performing assignment instead of equality test. In simple cases often warned by the compiler; in many languages, deliberately guarded against by language syntax

Resource bugs

• Null pointer dereference
• Using an uninitialized variable
• Using an otherwise valid instruction on the wrong data type (see packed decimal/binary coded decimal)
• Access violations
• Resource leaks, where a finite system resource such as memory or file handles are exhausted by repeated allocation without release.
• Buffer overflow, in which a program tries to store data past the end of allocated storage. This may or may not lead to an access violation or storage violation. These bugs can form a security vulnerability.
• Excessive recursion which though logically valid causes stack overflow

Multi-threading programming bugs

• Deadlock
• Race condition
• Concurrency errors in Critical sections, Mutual exclusions and other features of concurrent processing. Time-of-check-to-time-of-use (TOCTOU) is a form of unprotected critical section.

Teamworking bugs

• Unpropagated updates; e.g. programmer changes "myAdd" but forgets to change "mySubtract", which uses the same algorithm. These errors are mitigated by the Don't Repeat Yourself philosophy.
• Comments out of date or incorrect: many programmers assume the comments accurately describe the code
• Differences between documentation and the actual product

Bugs in popular culture

• In the 1968 novel 2001: A Space Odyssey (and the corresponding 1968 film), a spaceship's onboard computer, HAL 9000, attempts to kill all its crew members. In the followup 1982 novel, 2010: Odyssey Two, and the accompanying 1984 film, 2010, it is revealed that this action was caused by the computer having been programmed with two conflicting objectives: to fully disclose all its information, and to keep the true purpose of the flight secret from the crew; this conflict caused HAL to become paranoid and eventually homicidal.
• In the 1984 song 99 Red Balloons (though not in the original German version), "bugs in the software" lead to a computer mistaking a group of balloons for a nuclear missile and starting a nuclear war.
• The 2004 novel The Bug, by Ellen Ullman, is about a programmer's attempt to find an elusive bug in a database application.