More or less. I don’t think declaring your own memcpy ‘inline’ will get you all the benefits of using the ‘real’ one. If you want your compiler to know what me

More or less. I don’t think declaring your own memcpy ‘inline’ will get you all the benefits of using the ‘real’ one. If you want your compiler to know what memcpy does, so that, for example, it can compile it as an inlined “load register, store register” instruction pair _if_ it knows it’s copying 8 bytes, you have to #include<string.h> (with the angle brackets; #include "string.h" won’t do) So, if you want optimal performance, you can’t do without the compiler header. You’re still free to link with your own implementation of memcpy, of course, but don’t expect it to be called in all places where the source code contains calls to it.