Undefined Behavior in C and C++

15 days ago

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Undefined behavior (UB) in C and C++ refers to situations where the language standard imposes no requirements, allowing compilers to assume such behavior won't occur and optimize accordingly.
Common sources of UB include dereferencing bad pointers, signed integer overflow, uninitialized data usage, incorrect bit shifting, and strict aliasing violations.
UB exists primarily to enable compiler optimizations, not due to hardware differences, as it allows compilers to make assumptions that lead to more efficient code.
Examples of UB include signed integer overflow, where compilers may optimize away overflow checks, assuming they can't happen per the language rules.
Tools to mitigate UB risks include compiler warnings, sanitizers (like Valgrind), static analyzers, and safety flags (e.g., -fwrapv, -ftrapv).
In some cases, turning off optimization (-O0) or using a different language (e.g., Rust, Ada) may be practical strategies to avoid UB pitfalls.
UB can lead to security vulnerabilities and unpredictable behavior, making it critical to understand and avoid in low-level programming.

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