Why should strncpy() generally be avoided?

There is occasionally a good reason to use strncpy(). However:

• Using strncpy() into a large buffer can be very inefficient. strncpy() always writes to every byte in the destination buffer, which can waste a lot of time if the destination buffer is much longer than the source string.

  I once made critical code several times faster simply by recognizing that the previous programmer had copied short strings with strncpy (a, b, 4096); and fixing it.

• If the source string is longer than the size of the destination buffer, then strncpy() doesn't write a terminating null. So a call to strncpy() must be followed by explicitly writing a null terminator at the end of the destination buffer in most cases.