Reason: it's too difficult to use correctly (among the many, many mistakes you will make, think of the meaning of the N parameter: it's how many characters you can append).
Edit: see http://the-flat-trantor-society.blogspot.it/2012/03/no-strncpy-is-not-safer-strcpy.html for a more detailed explanation of what it was designed to do and how it's different from typical usage.
Better alternatives are OpenBSD's strlcat, or better(!!!) something like Microsoft' strcat_s/strncat_s -- it's better in that it returns wether an overflow occurred, so you can't make typos comparing to the wrong size; the downsize is that by default it aborts on overflow...
An even simpler alternative imho is http://yarchive.net/comp/linux/strncpy.html
Reason: it's too difficult to use correctly (among the many, many mistakes you will make, think of the meaning of the N parameter: it's how many characters you can append).
Edit: see http://the-flat-trantor-society.blogspot.it/2012/03/no-strncpy-is-not-safer-strcpy.html for a more detailed explanation of what it was designed to do and how it's different from typical usage.
Better alternatives are OpenBSD's strlcat, or better(!!!) something like Microsoft' strcat_s/strncat_s -- it's better in that it returns wether an overflow occurred, so you can't make typos comparing to the wrong size; the downsize is that by default it aborts on overflow...
An even simpler alternative imho is http://yarchive.net/comp/linux/strncpy.html