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The C and C++ standards allow writing portable code that shares values across a <code>[[setjmp|longjmp]]</code> in <code>volatile</code> objects, and the standards allow writing portable code that shares values between signal handlers and the rest of the code in <code>volatile</code> <code>sig_atomic_t</code> objects. Any other use of <code>volatile</code> keyword in C and C++ is inherently non-portable or incorrect. In particular, writing code with the <code>volatile</code> keyword for [[memory-mapped I/O]] devices is inherently non-portable and always requires deep knowledge of the specific target C/C++ implementation and platform.
=== Multi-
It is a common misconception that the <code>volatile</code> keyword is useful in portable [[thread (computing)|multi-threading]] code in C and C++. The <code>volatile</code> keyword in C and C++ has ''never'' functioned as a useful, portable tool for ''any'' multi-threading scenario.<ref>{{cite web |date=21 September 2021 |title=Volatile Keyword In Visual C++ |url=http://msdn2.microsoft.com/en-us/library/12a04hfd.aspx |work=Microsoft MSDN}}</ref><ref>{{cite web |title=Linux Kernel Documentation – Why the "volatile" type class should not be used |url=https://www.kernel.org/doc/html/latest/process/volatile-considered-harmful.html |work=kernel.org}}</ref><ref>{{cite web |author1=Scott Meyers |author2=Andrei Alexandrescu |year=2004 |title=C++ and the Perils of Double-Checked Locking |url=http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf |work=DDJ}}</ref><ref>{{cite web |author1=Jeremy Andrews |year=2007 |title=Linux: Volatile Superstition |url=http://kerneltrap.org/Linux/Volatile_Superstition |archive-url=https://web.archive.org/web/20100620121940/http://kerneltrap.org/Linux/Volatile_Superstition |archive-date=2010-06-20 |access-date=Jan 9, 2011 |publisher=kerneltrap.org}}</ref> Unlike the [[Java (programming language)|Java]] and [[C Sharp (programming language)|C#]] programming languages, operations on <code>volatile</code> variables in C and C++ are not [[atomic operation|atomic]], and operations on <code>volatile</code> variables do not have sufficient memory ordering guarantees (i.e. [[memory barrier|memory barriers]]). Most C and C++ compilers, linkers, and runtimes simply do not provide the necessary memory ordering guarantees to make the <code>volatile</code> keyword useful for ''any'' multi-threading scenario. Before the C11 and C++11 standards, programmers were forced to rely on guarantees from the individual implementations and platforms (e.g. POSIX and WIN32) to write [[thread (computing)|multi-threading]] code. With the modern C11 and C++11 standards, programmers can write portable [[thread (computing)|multi-threading]] code using new portable constructs such as the <code>std::atomic<T></code> templates.<ref>{{cite web |title=volatile (C++) |url=https://msdn.microsoft.com/en-us/library/12a04hfd.aspx |work=Microsoft MSDN|date=21 September 2021 }}</ref>
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=== Standards
While intended by both C and C++, the current C standard fails to express that the <code>volatile</code> semantics refer to the lvalue, not the referenced object. The respective defect report ''DR 476'' (to C11) is still under review with [[C17 (C standard revision)|C17]].<ref>[http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2244.htm ''Clarification Request Summary for C11.''] Version 1.13, October 2017.</ref>
=== Compiler
Unlike other language features of C and C++, the <code>volatile</code> keyword is not well supported by most C/C++ implementations - even for portable uses according to the C and C++ standards. Most C/C++ implementations are buggy regarding the behavior of the <code>volatile</code> keyword.<ref>{{Cite journal |last1=Eide |first1=Eric |last2=Regehr |first2=John |date=October 2008 |title=Volatiles Are Miscompiled, and What to Do about It |url=https://users.cs.utah.edu/~regehr/papers/emsoft08-preprint.pdf |journal=Proceedings of the Eighth ACM and IEEE International Conference on Embedded Software (EMSOFT), Atlanta, Georgia, USA |via=cs.utah.edu}}</ref><ref>{{Cite web |title=Volatile Bugs, Three Years Later – Embedded in Academia |url=https://blog.regehr.org/archives/503 |access-date=2024-08-28 |website=blog.regehr.org}}</ref> Programmers should take great care whenever using the <code>volatile</code> keyword in C and C++.
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Together, these guarantees make <code>volatile</code> into a useful [[thread (computing)|multi-threading]] construct in [[Java programming language|Java]]. In particular, the typical [[double-checked locking]] algorithm with <code>volatile</code> works correctly in [[Java programming language|Java]].<ref>{{cite web |author1=Neil Coffey |title=Double-checked Locking (DCL) and how to fix it |url=http://www.javamex.com/tutorials/double_checked_locking_fixing.shtml |access-date=2009-09-19 |publisher=Javamex}}</ref>
=== Early
Before Java version 5, the Java standard did not guarantee the relative ordering of <code>volatile</code> and non-<code>volatile</code> reads and writes. In other words, <code>volatile</code> did not have "acquire" and "release" [[memory barrier]] semantics. This greatly limited its use as a [[thread (computing)|multi-threading]] construct. In particular, the typical [[double-checked locking]] algorithm with <code>volatile</code> did ''not'' work correctly.
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