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In C and C++, volatile is a type qualifier, like const, and is a part of a type (e.g. the type of a variable or field). The behavior of the volatile keyword in C and C++ is sometimes given in terms of suppressing optimizations of an optimizing compiler: 1- don't remove existing volatile reads and writes, 2- don't add new volatile reads and writes, and 3- don't reorder volatile reads and writes.
As of 2014 and C11, there are four type qualifiers in standard C: const , volatile , restrict and _Atomic – the latter has a private name to avoid clashing with user-defined names. [3] The first two of these, const and volatile, are also present in C++, and are
constinit keyword; changes to concepts (removal of -> Type return-type-requirements [106]) (most of) volatile has been deprecated [59] DR: [[nodiscard]] effects on constructors [107] The new standard library concepts will not use PascalCase (rather standard_case, as the rest of the standard library) [108]
In C and C++, the volatile keyword was intended to allow C and C++ programs to directly access memory-mapped I/O. Memory-mapped I/O generally requires that the reads and writes specified in source code happen in the exact order specified with no omissions. Omissions or reorderings of reads and writes by the compiler would break the ...
There are valid forms of the pattern, including the use of the volatile keyword in Java and explicit memory barriers in C++. [4] The pattern is typically used to reduce locking overhead when implementing "lazy initialization" in a multi-threaded environment, especially as part of the Singleton pattern. Lazy initialization avoids initializing a ...
Which registers the called function must preserve for the caller (also known as: callee-saved registers or non-volatile registers) How the task of preparing the stack for, and restoring after, a function call is divided between the caller and the callee; This is intimately related with the assignment of sizes and formats to programming-language ...
Steven S. Muchnick, Advanced Compiler Design and Implementation (Morgan Kaufmann, 1997) pp. 378–396; John Cocke. "Global Common Subexpression Elimination." Proceedings of a Symposium on Compiler Construction, ACM SIGPLAN Notices 5(7), July 1970, pages 850–856.
Note the volatile keyword. In absence of volatile, the compiler and/or the CPU(s) may optimize access to lock and/or use cached values, thus rendering the above code erroneous. Conversely, and unfortunately, the presence of volatile does not guarantee that reads and writes are committed to memory.