strdup, strndup, strdupa, strndupa — duplicate a string


#include <string.h>

char *strdup(const char *s);

char *strndup(const char *s, size_t n);
char *strdupa(const char *s);
char *strndupa(const char *s, size_t n);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


   || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
   || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


Since glibc 2.10:

_POSIX_C_SOURCE >= 200809L

Before glibc 2.10:


strdupa(), strndupa(): _GNU_SOURCE


The strdup() function returns a pointer to a new string which is a duplicate of the string s. Memory for the new string is obtained with malloc(3), and can be freed with free(3).

The strndup() function is similar, but copies at most n bytes. If s is longer than n, only n bytes are copied, and a terminating null byte ('\0') is added.

strdupa() and strndupa() are similar, but use alloca(3) to allocate the buffer. They are available only when using the GNU GCC suite, and suffer from the same limitations described in alloca(3).

Return Value

On success, the strdup() function returns a pointer to the duplicated string. It returns NULL if insufficient memory was available, with errno set to indicate the cause of the error.



Insufficient memory available to allocate duplicate string.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
strdup(), strndup(), strdupa(),
Thread safety MT-Safe

Conforming to

strdup() conforms to SVr4, 4.3BSD, POSIX.1-2001. strndup() conforms to POSIX.1-2008. strdupa() and strndupa() are GNU extensions.

See Also

alloca(3), calloc(3), free(3), malloc(3), realloc(3), string(3), wcsdup(3)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

ecalloc(3), gd_entry(3), gd_strtok(3), guestfs-hacking(1), ldap_memfree(3), libnbd(3), mandoc_malloc(3), mm(3), pmdaDaemon(3), pmdaFetch(3), pmemobj_alloc(3), pmTraversePMNS(3), strcpy(3), string(3), talloc_string(3), vmem_malloc(3), wcsdup(3).

The man pages strdupa(3), strndup(3) and strndupa(3) are aliases of strdup(3).

2019-03-06 GNU Linux Programmer's Manual