I never said memcpy() wasn't standard. Only that strncpy() was also.
The difference in choice is this: do you own/did you allocate the memory you are accessing? If not, you may very well be playing with fire to try reading (or writing) past the end of memory you have not allocated.

The strncpy() function always pads the target out to n bytes. However, it stops reading the source when it hits the end of the string, which the C specification guarantees to be there in argv[].

You are correct about watching the end of string, as strncpy() does not guarantee that the target is null-terminated.

I will agree that the use of strncat() is the best choice so far, since it addresses both issues nicely.

The strtol() has the same validation problems as stroi(). Just because it returns something different... But you are right in that it is a little more convenient for catching incomplete conversions...

Cheers.