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copied!<p><strong>EDIT 1:</strong> The last drafts of C11 and C++11 are available online here: <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf" rel="noreferrer">C11 draft N1570</a> and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf" rel="noreferrer">C++11 draft n3242</a> if you don't have a copy of the final standards and wonderful what they look like. (Other adjustments to text appearance and some wording/grammar edits have been done.)</p> <p><strong>EDIT 2:</strong> Fixed all occurrences of "behaviour" to be "behavior" to match the standard.</p> <p>Searching the C++11 and C11 standards there are no matches for <em>indeterminate rule</em> or <em>undefined rule</em>. There are terms like <em>indeterminate value</em>, <em>indeterminately sequenced</em>, <em>indeterminate uninitialized</em>, etc.</p> <p>If talk of traps and exceptions seems weird in Norman Gray's answer, know that those terms do reflect the relevant definitions in <strong>Section 3</strong> in the <strong>C11 standard</strong>.</p> <p>C++ relies on C's definitions. Many useful definitions concerning types of <em>behaviour</em> can be found in C11's Section 3 (in C11). For example, <em>indeterminate value</em> is defined in 3.19.2. Do take note that C11's Section 2 (Normative References) provides other sources for additional terminology interpretation and Section 4 defines when cases such as <em>undefined behavior</em> occur as a result of <em>not complying</em> with the standard.</p> <p>C11's section 3.4 defines <em>behavior</em>, 3.4.1 defines <em>implementation-defined behavior</em>, 3.4.2 defines <em>locale-specific behavior</em>, 3.4.3 defines <em>undefined behavior</em>, 3.4.4 defines <em>unspecified behavior</em>. For <em>value</em> (Section 3.19), there are <em>implementation-defined value</em>, <em>indeterminate value</em>, and <em>unspecified value</em>.</p> <p>Loosely speaking, the term <strong>indeterminate</strong> refers to an <em>unspecified/unknown state</em> that by itself doesn't result in <em>undefined behavior</em>. For example, this C++ code involves an indeterminate value: { int x = x; }. (This is actually an example in the C++11 standard.) Here x is defined to be an integer first but at that point it does not have a well-defined value --then it is initialized to whatever (indeterminate/unknown) value it has!</p> <p>The well-known term <strong>undefined behavior</strong> is defined in 3.4.3 in C11 and refers to any situation of a </p> <blockquote> <p>nonportable or erroneous program construct or of erroneous data, for which this International Standard imposes no requirements</p> </blockquote> <p>In other words <em>undefined behavior</em> is some error (in logic or state) and whatever happens next is unknown! So one could make an <strong>undefined [behavior] rule</strong> that states: avoid undefined behavior when writing C/C++ code! :-)</p> <p>An <strong>indeterminate [behavior] rule</strong> would be to state: avoid writing indeterminate code <em>unless</em> it is needed <em>and</em> it does not affect program correctness or portability. So unlike undefined behavior, indeterminate behavior <em>does not necessarily</em> imply that code/data is erroneous, however, <em>its subsequent use may or may not be erroneous</em> --so care is required to ensure program correctness is maintained.</p> <p>Other terms like <em>indeterminately sequenced</em> are in the body text (e.g., C11 5.1.2.3 para 3; C++11, section 1.9 para. 13; i.e., in [intro.executation]). (As you might guess, it refers an unspecified order of operational steps.)</p> <p>IMO if one is interested in all of these nuances, acquiring both the C++11 and C11 standards is a must. This will permit one to explore to the desired level-of-detail needed with definitions, etc. If you don't have such the links provided herein will help you explore such with the last published draft C11 and C++11 standards.</p>

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