memcpy in place array copy

First look at a piece of code

#include <stdio.h>#include<pthread.h>intMain () {intt1[Ten]; inti =0;  for(i; i<Ten; i++) {T1[i]=i; printf ("t1[%d] =%d\n", I, t1[i]); } printf ("\ n"); memcpy (&t1[0], &t1[2],5*sizeof(int)); I=0;  for(i; i<5; i++) {printf ("t1[%d] =%d\n", I, t1[i]); }    return 0;}

I ran the ubuntu16.04, and the output was:

t1[02t1[13t1[24t1[3 5 t1[46

But the same program runs on ubuntu14.04 's virtual machine, and the result is:

t1[02t1[15t1[24t1[3 5 t1[46

The copy in the Mempcy group appears to be unsafe. Further research is needed.

Different companies have different implementations of stdlib function, and copies like this memory overlap need to use API Memmove () instead of memcpy.
In principle, when memory overlaps, the content is replicated in a buffer-like place, and the contents of the buffer are overwritten with dest memory. The efficiency will be slower than memcpy.

memcpy in place array copy