STRDUP(3) Library Functions Manual STRDUP(3)

strdup strndup — duplicate a specific number of bytes from a string


#include <string.h>

char *strdup(const char *s);
char *strndup(const char *s, size_t size);

The strdup () function shall return a pointer to a new string, which is a duplicate of the string pointed to by s. The returned pointer can be passed to free(3). A null pointer is returned if the new string cannot be created.

The strndup () function shall be equivalent to the strdup () function, duplicating the provided s in a new block of memory allocated as if by using malloc(3), with the exception being that strndup () copies at most size bytes from the array s into the newly allocated memory, terminating the new string with a null byte. If s contains a null terminator within the first size bytes, all bytes in s up to and including the null terminator shall be copied into the new memory buffer. The strndup () function shall not examine more than size bytes of the array pointed to by s. The newly created string shall always be properly terminated.

The strdup () function shall return a pointer to a new string on success. Otherwise, it shall return a null pointer and set errno to indicate the error.

Upon successful completion, the strndup () function shall return a pointer to the newly allocated memory containing the duplicated string. Otherwise, it shall return a null pointer and set errno to indicate the error.

These functions shall fail if:

Storage space available is insufficient.

None.

For functions that allocate memory as if by malloc(3), the application should release such memory when it is no longer required by a call to free(3). For strdup () and strndup (), this is the return value.

Implementations are free to malloc(3) a buffer containing either ( size + 1) bytes or ( ( s, size) + 1) bytes. Applications should not assume that strndup () will allocate ( size + 1) bytes when ( s) is smaller than size.

None.

None.

free(3), wcsdup(3)

XBD <string.h>

First released in Issue 4, Version 2.

Moved from X/OPEN UNIX extension to BASE.

Austin Group Interpretation 1003.1-2001 #044 is applied, changing the "may fail" [ENOMEM] error to become a "shall fail" error.

The strdup () function is moved from the XSI option to the Base.

The strndup () function is added from The Open Group Technical Standard, 2006, Extended API Set Part 1.

The APPLICATION USAGE section is updated to clarify that memory is allocated as if by malloc(3).

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0338 [738] is applied.

Austin Group Defect 1019 is applied, clarifying that the strndup () argument s need not point to a null-terminated string.

June 14, 2024 posix.fail