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C++ STL Array vs. Vector: Raw Element Access Performance Deep Dive

This tutorial explores the performance differences between accessing elements in `std::array`, `std::vector`, and raw C-style arrays in C++, focusing specifically on raw element access using indexing (`[]` operator) and pointer arithmetic. We'll cover theoretical underpinnings, practical benchmarks, compiler optimizations, and best practices.

*1. Understanding the Basics*

Before diving into performance comparisons, let's quickly review the core characteristics of each data structure:

*`std::array`**: A fixed-size array that is a *template class wrapper around a primitive C-style array. Its size is determined at compile time. It provides type safety, bounds checking when you use the `.at()` method (but not with `[]` indexing), and iterator support compared to a raw array. The storage is contiguous in memory, just like a raw C array.

*`std::vector`**: A dynamic array that can grow or shrink at runtime. It manages its own memory allocation. `std::vector` also offers type safety, bounds checking with `at()`, and iterator support. The storage is *contiguous in memory. When the vector's capacity is exceeded, it usually reallocates a larger block of memory and copies all elements. This reallocation can have performance implications, but we are not focusing on reallocation cost for this tutorial.

*Raw C-style array (e.g., `int arr[100]`):* The most fundamental array type. It's a contiguous block of memory that holds elements of the same type. Raw arrays lack built-in bounds checking, type safety beyond the type of the array, and other features provided by `std::array` and `std::vector`. They are typically allocated on the stack (if declared within a function) or statically (if declared globally). Dynamic allocation is also possible via `new`/`delete`.

*2. Theoretical Performance Expectations for Raw Access*

In theory, for raw access (i.e., using the `[]` operator d ...

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