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.

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Last updated 02 Jan 2004 23:40. Copyright © 2004 Ben Pfaff.
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