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.
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 strncmp() function shall compare not more than n bytes (bytes
that follow a NUL character are not compared) from the array pointed
to by s1 to the array pointed to by s2.
The sign of a non-zero return value is determined by the sign of the
difference between the values of the first pair of bytes (both
interpreted as type unsigned char) that differ in the strings being
Upon successful completion, strncmp() shall return an integer greater
than, equal to, or less than 0, if the possibly null-terminated array
pointed to by s1 is greater than, equal to, or less than the possibly
null-terminated array pointed to by s2 respectively.
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 STRNCMP(3P)