It only helps so much.

I've taught to freshmen students who have personally encountered dozens of different false positives and false negatives not only with sanitizers, but with compiler warnings as well. Nothing extraordinary, just `-Wall -Wextra -Werror` with the latest available GCC/Clang on the latest available Ubuntu LTS.

Some examples (some library bugs are also included):

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98677

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105729

https://github.com/llvm/llvm-project/issues/59432

https://github.com/boostorg/dll/issues/30

https://github.com/boostorg/asio/commit/71964b22c7fade69cc4c...

https://github.com/chriskohlhoff/asio/issues/997

I've also seen fun examples of a program working with all sanitizers in 14 modes across 3 OSes (GCC and Clang on Ubuntu, Apple Clang on macOS, Visual Studio on Windows), and _only_ failing with Visual Studio Release mode. It was an array overflow. Just was not caught by sanitizers.

Mind you: no weird C++ magic, just standard coding exercises.

ubsan is awesome, but it's not too hard to construct programs that contain undefined behavior that -fsanitize=undefined won't catch.