apue 4.23 path_alloc未定义的引用问题

很曲折，显示“path_alloc未定义的引用问题”，于是我准备做一个静态库，但是做了半天没做出来，只好跟以前一样乖乖把2-16的代码复制过来。

然后发现书上这个路径不太对，
/var/spool/uucppublic貌似是为了说明chdir跟随符号链接，但是我ubuntu
中chdir不了这个目录。原因未知。。。现在发现做什么都做不了，好好学习吧。。

代码。。

#include "apue.h"
#include "apue.h"
#include 
#include 

#ifdef  PATH_MAX
static long pathmax = PATH_MAX;
#else
static long pathmax = 0;
#endif

static long posix_version = 0;
static long xsi_version = 0;

/* If PATH_MAX is indeterminate, no guarantee this is adequate */
#define PATH_MAX_GUESS  1024

char *
path_alloc(size_t *sizep) /* also return allocated size, if nonnull */
{
    char    *ptr;
    size_t  size;

    if (posix_version == 0)
        posix_version = sysconf(_SC_VERSION);

    if (xsi_version == 0)
        xsi_version = sysconf(_SC_XOPEN_VERSION);

    if (pathmax == 0) {     /* first time through */
        errno = 0;
        if ((pathmax = pathconf("/", _PC_PATH_MAX)) < 0) {
            if (errno == 0)
                pathmax = PATH_MAX_GUESS;   /* it's indeterminate */
            else
                err_sys("pathconf error for _PC_PATH_MAX");
        } else {
            pathmax++;      /* add one since it's relative to root */
        }
    }

    /*
     * Before POSIX.1-2001, we aren't guaranteed that PATH_MAX includes
     * the terminating null byte.  Same goes for XPG3.
     */
    if ((posix_version < 200112L) && (xsi_version < 4))
        size = pathmax + 1;
    else
        size = pathmax;

    if ((ptr = malloc(size)) == NULL)
        err_sys("malloc error for pathname");

    if (sizep != NULL)
        *sizep = size;
    return(ptr);
}

int
main(void)
{
    char    *ptr;
    size_t      size;

    if (chdir("/home/xc/test1") < 0)
        err_sys("chdir failed");

    ptr = path_alloc(&size);    /* our own function */
    if (getcwd(ptr, size) == NULL)
        err_sys("getcwd failed");

    printf("cwd = %s\n", ptr);
    exit(0);
}