Undefined behaviour: the C/C++ hall of shame_

In C and C++, signed integer overflow is undefined behaviour — not wrap-around. Compilers exploit this to eliminate overflow checks entirely when optimizing. Use unsigned types or compiler flags like -fwrapv if you need wrap semantics.

The strict aliasing rule says you cannot access memory through a pointer of an incompatible type. The classic sin is casting a float* to an int* to inspect its bits. The correct way is memcpy or std::bit_cast in C++20.

AddressSanitizer and UndefinedBehaviorSanitizer catch most of these at runtime during testing. Compile with -fsanitize=address,undefined and run your test suite. The performance hit is worth it for debug builds. Do this before shipping anything.

Use-after-free bugs dominate security vulnerability lists every year. Modern C++ smart pointers (unique_ptr, shared_ptr) eliminate most of them but you have to actually use them — raw new/delete in application code is a code smell in 2024.