strlcpy(3)                                                   strlcpy(3)

  strlcpy()

  NAME

    strlcpy, strlcat - size-bounded string copying and concatenation

  SYNOPSIS

    #include 

    size_t  strlcpy(char *dst, const char *src, size_t size);

    size_t  strlcat(char *dst, const char *src, size_t size);

  DESCRIPTION

    The strlcpy() and strlcat() functions copy and concatenate strings
    respectively. They are designed to be safer, more consistent, and less
    error prone replacements for strcpy(3) and strncat(3). Unlike those
    functions, strlcpy() and strlcat() take the full size of the buffer (not
    just the length) and guarantee to NUL-terminate the result (as long as
    size is larger than 0). Note that you should include a byte for the NUL in
    size.

    The strlcpy() function copies up to size - 1 characters from the NUL-
    terminated string src to dst, and NUL-terminating the result.

    The strlcat() function appends the NUL-terminated string src to the end of
    dst. It will append at most (size - strlen(dst) - 1) bytes, and NUL-
    terminating the result.

  RETURN VALUES

    The strlcpy() and strlcat() functions return the total length in bytes of
    the string they tried to create, not including the NUL terminator.

    For strlcpy() that means the length of src.

    For strlcat() that means the initial length of dst plus the length of src.

    Because this return value is the total potential length, it is easy to
    detect when truncation happens in dst by comparing this value to size.

  EXAMPLES

    The following code fragment illustrates the simple case:

    char *s, *p, buf[BUFSIZ];
    ...
    (void)strlcpy(buf, s, sizeof(buf));
    (void)strlcat(buf, p, sizeof(buf));

    To detect truncation, perhaps while building a pathname, something like
    the following might be used:

    char *dir, *file, pname[MAXPATHNAMELEN];
    ...
    if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
            goto toolong;
    if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
            goto toolong;

    Since we know how many characters we copied the first time, we can speed
    things up a bit by using a copy instead on an append:

    char *dir, *file, pname[MAXPATHNAMELEN];
    size_t n;
    ...
    n = strlcpy(pname, dir, sizeof(pname));
    if (n >= sizeof(pname))
            goto toolong;
    if (strlcpy(pname + n, file, sizeof(pname) - n) >=sizeof(pname) - n)
            goto toolong;

    However, one may question the validity of such optimizations, as they
    defeat the whole purpose of strlcpy() and strlcat(). As a matter of fact,
    the first version of this manual page got it wrong.

  SEE ALSO

    snprntf(3)

    strcat(3)

    strncpy(3)

  USAGE NOTES

    All of these functions are thread safe.

    None of these functions are async-signal safe.