This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
For strncpy(): The functionality described on this reference page is
aligned with the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional.
This volume of POSIX.1‐2008 defers to the ISO C standard.
The stpncpy() and strncpy() functions shall copy not more than n
bytes (bytes that follow a NUL character are not copied) from the
array pointed to by s2 to the array pointed to by s1.
If the array pointed to by s2 is a string that is shorter than n
bytes, NUL characters shall be appended to the copy in the array
pointed to by s1, until n bytes in all are written.
If copying takes place between objects that overlap, the behavior is
If a NUL character is written to the destination, the stpncpy()
function shall return the address of the first such NUL character.
Otherwise, it shall return &s1[n].
The strncpy() function shall return s1.
No return values are reserved to indicate an error.
Applications must provide the space in s1 for the n bytes to be
transferred, as well as ensure that the s2 and s1 arrays do not
Character movement is performed differently in different
implementations. Thus, overlapping moves may yield surprises.
If there is no NUL character byte in the first n bytes of the array
pointed to by s2, the result is not null-terminated.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 STRNCPY(3P)