strdup(3) Library Functions Manual strdup(3)

strdup, strndup, strdupa, strndupa - duplicate a string

Standard C library (libc, -lc)

#include <string.h>
char *strdup(const char *s);
char *strndup(const char s[.n], size_t n);
char *strdupa(const char *s);
char *strndupa(const char s[.n], size_t n);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

strdup():

    _XOPEN_SOURCE >= 500
        || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

strndup():

    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE

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.

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 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 (), strndupa () Thread safety MT-Safe

POSIX.1-2008.
GNU.

SVr4, 4.3BSD-Reno, POSIX.1-2001.
POSIX.1-2008.
GNU.

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

2024-05-02 Linux man-pages 6.9