Because it is a function in the C Standard Library. Programs are typically prohibited from declaring these functions. You can if you don't link with libc and pa

Because it is a function in the C Standard Library. Programs are typically prohibited from declaring these functions. You can if you don't link with libc and pass in the correct compiler flags (gcc will turn some raw loops into a memcpy call as an optimization even without linking libc afaik) https://www.gnu.org/software/libc/manual/html_node/Reserved-Names.html https://www.gnu.org/software/libc/manual/html_node/Reserved-...