Memcpymemmove

Memcpymemmove is not a distinct standard function, but a compact reference to the two related memory-copy operations found in the C standard library: memcpy and memmove. These functions perform byte-wise copying of data from a source to a destination, but they differ in how they handle overlapping memory regions.

Memcpy copies n bytes from the source to the destination and assumes that the source and destination do not overlap. If the memory areas do overlap, the behavior is undefined, which means it can lead to data corruption and is not portable. memcpy is typically optimized for speed and may use architecture-specific instructions, alignment assumptions, or vectorized operations when overlap is not a concern.

Memmove copies n bytes from the source to the destination and is defined to handle overlapping regions safely. If src and dest overlap, memmove ensures that the original data is preserved, either by using a temporary buffer or by copying in an order (forward or backward) that prevents premature overwriting. When there is no overlap, memmove may be implemented identically to memcpy or with similar optimizations.

Usage guidelines: choose memcpy when you can guarantee that the source and destination do not overlap and you need high throughput. Choose memmove when there is a possibility of overlap or when portable, well-defined behavior is required across platforms. Both functions have prototypes similar to void *memcpy(void *dest, const void *src, size_t n) and void *memmove(void *dest, const void *src, size_t n), and both return a pointer to dest.

Implementation and correctness notes: implementations vary by library and architecture, so performance characteristics can differ. Be mindful of pointer validity, correct size_t usage, and the fact that these functions copy raw bytes, which may include non-text data. See also memcpy, memmove, and related routines in string.h.