The difference between memcopy and memmove

The memcopy and Memmove functions look at the source code of two functions under Linux.

Two functions are defined in the header file string.h, and the function prototype is:

void * __cdecl memcpy (void * dst,const void * src,size_t count);
void * __cdecl memmove (void * dst,const void * SR c,size_t count);

The implementation code is as follows:

void * __cdecl memcpy (void * dst,const void * src,size_t count) {void * ret = DST;
                   while (count--) {//Note that the memcpy function does not handle the problem of overlapping DST and SRC regions * (char *) DST = * (char *) src;
                   DST = (char *) DST + 1;
         src = (char *) src + 1;
return (ret);
         } void * __cdecl memmove (void * dst,const void * src,size_t count) {void * ret = DST; if (DST <= src | | (char *) DST >= ((char *) SRC + count) {//If the DST and src regions do not overlap, copy them at the beginning WH
                            Ile (count--) {* (char *) DST = * (char *) src;
                            DST = (char *) DST + 1;
                   src = (char *) src + 1; } else {//if the DST and SRC regions Cross, copy from the tail to the starting position to avoid data collisions DST = (char *) DST + cou
                   nt-1;
                   src = (char *) src + count-1; While (count--)
                            {* (char *) DST = * (char *) src;
                            DST = (char *) dst-1;
                   src = (char *) src-1;
} return (ret); }

To sum up:

When the SRC and DST regions do not overlap, two functions are exactly the same. The wood has overlapping conditions: DST <= src | | (char *) DST >= ((char *) SRC + count. Otherwise, memcpy is not working properly, memmove can work normally.