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Across an application the penalty is normally 1-5%. Most business code benefits from the increased safety. Parsers are an exception, but the large attack surface sometimes makes it a good idea there too.

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If you are quoting the numbers google put out, recall that those numbers were after they profiled and manually disabled bounds checks in cases where it caused significant slowdown.. so in other words the numbers were garbage.

The bigger problem is that std::vector::at() is kinda useless in any case since it's very rare in idiomatic C++ to be indexing into a vector using an integer. You're much more likely to be using an iterator, since that's what you'll get from standard algorithms like std::find() etc. And there's no API for "checked iterators" that is equivalent to at(). For a debug build, your STL implementation might use checked iterators, but that's a quality of implementation matter that you can't rely on.

MSVC does have a documented checked iterator facility that can be enabled even in release builds: https://learn.microsoft.com/en-us/cpp/standard-library/check....

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