< c‎ | experimental‎ | dynamic
Defined in header <string.h>
char * strdup(const char *str1);
(dynamic memory TR)

Returns a pointer to a null-terminated byte string, which is a duplicate of the string pointed to by str1. The returned pointer must be passed to free to avoid a memory leak.

If an error occurs, a null pointer is returned and errno may be set.

As all functions from Dynamic Memory TR, strdup is only guaranteed to be available if __STDC_ALLOC_LIB__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT2__ to the integer constant 1 before including string.h.


str1 - pointer to the null-terminated byte string to duplicate

Return value

A pointer to the newly allocated string, or a null pointer if an error occurred.


The function is identical to the POSIX strdup.


#ifdef __STDC_ALLOC_LIB__
#define __STDC_WANT_LIB_EXT2__ 1
#define _POSIX_C_SOURCE 200809L
#include <string.h>
#include <assert.h>
#include <stdlib.h>
int main(void)
    const char *s1 = "String";
    char *s2 = strdup(s1);
    assert(strcmp(s1, s2) == 0);

See also

(dynamic memory TR)
allocate a copy of a string up to specified size
copies one string to another
allocates memory