Int a = 5; a = a++ + ++a; a =? (2011)
3 days ago
- #Increment Operators
- #Compiler Differences
- #Undefined Behavior
- The expression a = a++ + ++a exhibits undefined behavior in C/C++ due to unsequenced modifications and accesses of variable 'a'.
- Two undefined behavior issues are identified: the order of fetching and pre-increment, and the handling of post-increment relative to assignment.
- Possible results from different evaluation orders include 11, 12, and 13, with specific compiler implementations yielding varying outcomes.
- Empirical testing across compilers shows results such as 11, 12, 13, and 14 for related expressions, highlighting inconsistent compiler behavior.
- Examples include gcc typically outputting 11, 12, or 13; clang and Java often produce 11 or 12; while C# has well-defined left-to-right evaluation.
- Overloaded operators in C++ can alter results compared to built-in operators, as shown with Microsoft C/C++ and g++ tests.
- The code provided is intended for compiler testing, emphasizing the unpredictability of such expressions in undefined behavior contexts.