Why is strnlen() not considered for inclusion in C23?

Question

Functions strdup() and strndup() have finally made it into the upcoming C23 Standard:

7.24.6.4 The strdup function

Synopsis

#include <string.h>
char *strdup(const char *s);

The strdup function creates a copy of the string pointed to by s in a space allocated as if by a call to malloc.

Returns
The strdup function returns a pointer to the first character of the duplicate string. The returned pointer can be passed to free. If no space can be allocated the strdup function returns a null pointer.

7.24.6.5 The strndup function

Synopsis

#include <string.h>
char *strndup(const char *s, size_t size);

The strndup function creates a string initialized with no more than size initial characters of the array pointed to by s and up to the first null character, whichever comes first, in a space allocated as if by a call to malloc. If the array pointed to by s does not contain a null within the first size characters, a null is appended to the copy of the array.

Returns
The strndup function returns a pointer to the first character of the created string. The returned pointer can be passed to free. If no space can be allocated the strndup function returns a null pointer.

Why was the POSIX-2008 function strnlen not considered for inclusion?

#include <string.h>
size_t strnlen(const char *s, size_t maxlen);

The strnlen() function shall compute the smaller of the number of bytes in the array to which s points, not including the terminating NUL character, or the value of the maxlen argument. The strnlen() function shall never examine more than maxlen bytes of the array pointed to by s.

Answer 1

Interesingly, this function was proposed in https://www9.open-std.org/JTC1/SC22/WG14/www/docs/n2351.htm

It was discussed at the London meeting in 2019. See the agenda: https://www9.open-std.org/JTC1/SC22/WG14/www/docs/n2370.htm

The discussion minutes can be found at https://www9.open-std.org/JTC1/SC22/WG14/www/docs/n2377.pdf. Page 59.

It was rejected due to no consensus.

6.33 Sebor, Add strnlen to C2X [N 2351]

...

*Straw poll: Should N2351 be put into C2X?

(11/6/6)

Not clear consensus.

As result the function was not added.

Answer 2

One argument against strnlen is that it's a superfluous function, since we already have memchr. Example:

const char str[666] = "hello world";
size_t length1 = strnlen(str,666);
size_t length2 = (char*)memchr(str,'\0',666) - str;

Advantages of memchr:

• Already been a standard C function since the dawn of time.
• Possibly more efficient than strnlen in some situations(?).
• More generic API.
• memchr already ought to be in use for the purpose of sanitising supposed string input before calling functions like strcpy, so what purpose strnlen fills is unclear.
• Has proper error handling, unlike strnlen which does not tell if it failed or not.

Disadvantages:

• More awkward and type-unsafe interface for the purpose of finding a string length specifically.