Editing Undefined behavior (section)

{{verify|date=February 2025}}
{{Short description|Unpredictable result when running a program}}
{{Distinguish|Undefined value|Unspecified behavior}}
In [[computer programming]], a program exhibits '''undefined behavior''' ('''UB''') when it contains, or is executing code for which its [[programming language specification]] does not mandate any specific requirements.<ref>{{cite web|title=What Every C Programmer Should Know About Undefined Behavior #1/3|date=13 May 2011 |url=https://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html|access-date=23 February 2025}}</ref> This is different from [[unspecified behavior]], for which the language specification does not prescribe a result, and implementation-defined behavior that defers to the documentation of another component of the [[computing platform|platform]] (such as the [[application binary interface|ABI]] or the [[translator (computing)|translator]] documentation).

In the [[C (programming language)|C programming community]], undefined behavior may be humorously referred to as "'''nasal demons'''", after a [[comp.* hierarchy|comp.std.c]] post that explained undefined behavior as allowing the compiler to do anything it chooses, even "to make demons fly out of your nose".<ref>{{cite web|title=nasal demons|url=http://catb.org/jargon/html/N/nasal-demons.html|website=[[Jargon File]]|access-date=12 June 2014}}</ref>