Section: POSIX Programmer's Manual (3P)
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.
--- duplicate a specific number of bytes from a string
char *strdup(const char *s);
char *strndup(const char *s, size_t size);
function shall return a pointer to a new string, which is a duplicate
of the string pointed to by
The returned pointer can be passed to
A null pointer is returned if the new string cannot be created.
function shall be equivalent to the
function, duplicating the provided
in a new block of memory allocated as if by using
with the exception being that
copies at most
plus one bytes into the newly allocated memory, terminating the new
string with a NUL character. If the length of
is larger than
bytes shall be duplicated. If
is larger than the length of
all bytes in
shall be copied into the new memory buffer, including the terminating
NUL character. The newly created string shall always be properly
function shall return a pointer to a new string on success. Otherwise,
it shall return a null pointer and set
to indicate the error.
Upon successful completion, the
function shall return a pointer to the newly allocated memory
containing the duplicated string. Otherwise, it shall return a null
pointer and set
to indicate the error.
These functions shall fail if:
Storage space available is insufficient.
The following sections are informative.
For functions that allocate memory as if by
the application should release such memory when it is no longer
required by a call to
this is the return value.
Implementations are free to
a buffer containing either (size
+ 1) bytes or (strnlen(
+ 1) bytes. Applications should not assume that
will allocate (size
+ 1) bytes when
is smaller than
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
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