strndup

 

C

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Technical Specifications

 

Strings library

Byte strings

Multibyte strings

Wide strings

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll (C99) strtolstrtoll (C99)	strtoulstrtoull (C99) strtofstrtodstrtold (C99)(C99) strtoimaxstrtoumax (C99)(C99)
String manipulation
strcpystrcpy_s (C11)
strncpystrncpy_s (C11)
strcatstrcat_s (C11)
strncatstrncat_s (C11)
strxfrm
strdup (C23)
strndup (C23)
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr
memcmp
memsetmemset_s (C11)
memcpymemcpy_s (C11)
memmovememmove_s (C11)
memccpy (C23)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

Defined in header <string.h>
char *strndup( const char *str1, size_t size );		(since C23)

Returns a pointer to a null-terminated byte string, which contains copies of at most size bytes from the string pointed to by str1. The space for the new string is obtained as if malloc was called. If the null terminator is not encountered in the first size bytes, it is appended to the duplicated string.

The returned pointer must be passed to free to avoid a memory leak.

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

Parameters

str1	-	pointer to the null-terminated byte string to duplicate
size	-	max number of bytes to copy from str1

Return value

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

Notes

The function is identical to the POSIX strndup except that it is allowed, but not required to set errno on error.

Example

Run this code

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    const size_t n = 3;
 
    const char *src = "Replica";
    char *dup = strndup(src, n);
    printf("strndup(\"%s\", %lu) == \"%s\"\n", src, n, dup);
    free(dup);
 
    src = "Hi";
    dup = strndup(src, n);
    printf("strndup(\"%s\", %lu) == \"%s\"\n", src, n, dup);
    free(dup);
 
    const char arr[] = {'A','B','C','D'}; // NB: no trailing '\0'
    dup = strndup(arr, n);
    printf("strndup({'A','B','C','D'}, %lu) == \"%s\"\n", n, dup);
    free(dup);
}

Output:

strndup("Replica", 3) == "Rep"
strndup("Hi", 3) == "Hi"
strndup({'A','B','C','D'}, 3) == "ABC"

See also

strdup (C23)	allocates a copy of a string (function)
strcpystrcpy_s (C11)	copies one string to another (function)
malloc	allocates memory (function)
free	deallocates previously allocated memory (function)