Undefined behavior

<p>In <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, a program exhibits undefined behavior (UB) when it contains, or is executing code for which its <a href="/facts/Programming_language_specification/XSTQ2W2s">programming language specification</a> does not mandate any specific requirements. This is different from <a href="/facts/Unspecified_behavior/1BdoC4KF">unspecified behavior</a>, for which the language specification does not prescribe a result, and implementation-defined behavior that defers to the documentation of another component of the <a href="/facts/Computing_platform/DmKwp5Bk">platform</a> (such as the <a href="/facts/Application_binary_interface/wc6pmKKb">ABI</a> or the <a href="/facts/Translator_(computing)/D3TIzmrI">translator</a> documentation).
</p><p>In the <a href="/facts/C_(programming_language)/Ky2No763">C programming community</a>, undefined behavior may be humorously referred to as "nasal demons", after a <a href="/facts/Comp.*_hierarchy/5eWLRV0C">comp.std.c</a> post that explained undefined behavior as allowing the compiler to do anything it chooses, even "to make demons fly out of your nose".
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Undefined behavior open-in-new

Undefined behavior