memoryoffset

Memory offset is a non-negative distance, usually measured in bytes, from a base address to a target memory location. It is a fundamental concept in memory addressing, used to locate elements within data structures, map devices, or calculate effective addresses in various programming and hardware contexts.

In programming, offsets arise when working with arrays, structures, or pointers. For an array base address B and an element with size S, the i-th element is located at B + i × S. For example, with 4-byte integers, the element at index i is at B + 4i. Pointer arithmetic in languages like C mirrors this idea: adding an integer n to a pointer advances the address by n elements, which corresponds to an offset of n × sizeof(element) bytes.

Offsets also appear in multi-dimensional arrays. The memory offset for an element depends on the array layout (row-major or column-major) and is computed from row and column indices, element size, and the total size of a row or column.

In CPU architectures, offsets are part of addressing modes such as base+offset (displacement) addressing. The effective address is formed by adding a base register value to a displacement, sometimes with an index register. This mechanism underpins accessing variables, stack frames, and operands in instruction sets.

Security and correctness considerations include ensuring offsets stay within allocated bounds to avoid out-of-bounds access, which can lead to crashes or vulnerabilities. Endianness affects how the bytes within a value are ordered, but not the offset itself, which specifies where the value starts.

Related concepts include memory address, pointer arithmetic, and addressing modes. Memory offsets are a core tool for efficient data access and low-level programming.