Note that STL containers allow you to bounds check "[]" indexing even in release mode if you set the right preprocessor directives. The flag differs between com

Note that STL containers allow you to bounds check "[]" indexing even in release mode if you set the right preprocessor directives. The flag differs between compilers and stdlib implementations, though. For libstdc++ (default on linux), use _GLIBCXX_ASSERTIONS. For example, the following code aborts on release builds too: // g++ -O3 -D_GLIBCXX_ASSERTIONS=1 file.cpp #include <iostream> #include <vector> int main() { std::vector<int> vec{1, 2, 3, 4}; std::cout << vec[4]; } MSVC provides similar functionality using the _ITERATOR_DEBUG_LEVEL directive. The point is that there is no inherent limitation that one has to use the .at() method for bounds checking STL container access.