Shift damn you.

So, im writing a c++ program and i have it all done encept for some reason i cannot get the idea behind shifting a string down.
so i was wondering how you code to get
abc...yz   to become
bcd...za?

void shift_str(char *str) {
 char a = str[0];
 int l=strlen(str);
 memmove(str,str+1,l);
 str[l]=a;
}