Volatile qualification
Volatile qualification is a type qualifier that tells the compiler accesses to an object may have observable effects and must not be freely eliminated or optimized as ordinary accesses.
Modern C, Third Edition
The C volatile qualifier specifies that accesses to an object may have externally observable effects and must not be treated as freely eliminable or cacheable by the compiler.
- How it is used
- Preserves necessary object accesses during optimization in measurements, long-jump recovery, and signal handling.
- How deep it goes
- Explains reloads and stores, then traces optimization consequences through assembly and exceptional control flow; distinguishes volatile access from uninterruptible operations.
- Examples
- Compares timed C loops and GCC and Clang assembly, then uses a volatile depth variable in a setjmp and longjmp example.
- What you can do after
- Diagnose/debug with it when optimization discards measurement work or makes assumptions about values changed across unusual control flow.
Read how Modern C, Third Edition explains volatile qualification →
Modern C
A volatile qualification is a C type qualifier indicating that an object's value may change independently of ordinary program execution and must not be optimized away from accesses.
- How it is used
- Preserves required object accesses in measurement loops and values used after setjmp/longjmp.
- How deep it goes
- Explains reloads, stores, and optimization costs through loop assembly and a longjmp repair; does not develop a general concurrency model.
- Examples
- Compares three timed loops and repairs a parser's nesting-depth diagnostic after longjmp.
- What you can do after
- Diagnose/debug with it an eliminated measurement loop or an incorrect value used after longjmp.
Related concepts
- performance optimizationcontrasts with · Performance optimization is the systematic modification of software or its operating conditions to improve measured execution speed, responsiveness, throughput, or resource efficiency while preserving required behavior.
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