Re: [PATCH v5 5/5] strncat.3: Rewrite to be consistent with string_copy.7.

[Alejandro Colomar <alx.manpages@gmail.com>]

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Formatted strncat(3):

strncat(3)                 Library Functions Manual                 strncat(3)

NAME
        strncat - concatenate a null‐padded character sequence into a string

LIBRARY
        Standard C library (libc, -lc)

SYNOPSIS
        #include <string.h>

        char *strncat(char *restrict dst, const char src[restrict .sz],
                       size_t sz);

DESCRIPTION
        This  function  catenates  the  input character sequence contained in a
        null‐padded fixed‐width buffer, into a string at the buffer pointed  to
        by  dst.   The  programmer is responsible for allocating a buffer large
        enough, that is, strlen(dst) + strnlen(src, sz) + 1.

        An implementation of this function might be:

            char *
            strncat(char *restrict dst, const char *restrict src, size_t sz)
            {
                int   len;
                char  *end;

                len = strnlen(src, sz);
                end = dst + strlen(dst);
                end = mempcpy(end, src, len);
                *end = '\0';

                return dst;
            }

RETURN VALUE
        strncat() returns dest.

ATTRIBUTES
        For an explanation of the terms  used  in  this  section,  see  attrib‐
        utes(7).
        ┌────────────────────────────────────────────┬───────────────┬─────────┐
        │Interface                                   │ Attribute     │ Value   │
        ├────────────────────────────────────────────┼───────────────┼─────────┤
        │strncat()                                   │ Thread safety │ MT‐Safe │
        └────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS
        POSIX.1‐2001, POSIX.1‐2008, C89, C99, SVr4, 4.3BSD.

CAVEATS
        The  name of this function is confusing.  This function has no relation
        to strncpy(3).

        If the destination buffer is not large enough, the  behavior  is  unde‐
        fined.  See _FORTIFY_SOURCE in feature_test_macros(7).

BUGS
        This function can be very inefficient.  Read about Shlemiel the painter
        ⟨https://www.joelonsoftware.com/2001/12/11/back-to-basics/⟩.

EXAMPLES
        #include <stdio.h>
        #include <stdlib.h>
        #include <string.h>

        int
        main(void)
        {
            char    buf[BUFSIZ];
            size_t  len;

            buf[0] = '\0';  // There’s no ’cpy’ function to this ’cat’.
            strncat(buf, "Hello XXX", 6);
            strncat(buf, "world", 42);
            strncat(buf, "!", 1);
            len = strlen(buf);

            printf("[len = %zu]: ", len);
            puts(buf);  // "Hello world!"

            exit(EXIT_SUCCESS);
        }

SEE ALSO
        string(3), string_copy(3)

Linux man‐pages (unreleased)        (date)                          strncat(3)

-- 
<http://www.alejandro-colomar.es/>

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