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.
strncmp — compare part of two strings
int strncmp(const char *s1, const char *s2, size_t n);
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.1‐2017 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.
No errors are defined.
The following sections are informative.
The Base Definitions volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
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