UNIX环境高级编程apue.h和err_sys报错处理

http://www.apuebook.com/code3e.html Source Code下载源码，将my_err.h文件放到/usr/include目录中，这时候依旧会出现下面的报错

/tmp/ccI0CaOT.o: In function `main':
stdinToStdout.c:(.text+0x3d): undefined reference to `err_sys'
stdinToStdout.c:(.text+0x52): undefined reference to `err_sys'
collect2: error: ld returned 1 exit status

这是因为err_quit和err_sys是作者自定义的函数，需要单独定义头文件，两种方式，一是将源码中error.c复制到/usr/include目录下，在apue.h文件中加#include "error.c"，另一种方式就是在/usr/include中建立myerr.h文件，#include 。

#include "apue.h"
#include  /* for definition of errno */
#include  /* ISO C variable aruments */
static void err_doit(int, int, const char *, va_list);
/*
* Nonfatal error related to a system call.
* Print a message and return.
*/
void
err_ret(const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(1, errno, fmt, ap);
    va_end(ap);
}
/*
* Fatal error related to a system call.
* Print a message and terminate.
*/
void
err_sys(const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(1, errno, fmt, ap);
    va_end(ap);
    exit(1);
}
/*
* Fatal error unrelated to a system call.
* Error code passed as explict parameter.
* Print a message and terminate.
*/
void
err_exit(int error, const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(1, error, fmt, ap);
    va_end(ap);
    exit(1);
}
/*
* Fatal error related to a system call.
* Print a message, dump core, and terminate.
*/
void
err_dump(const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(1, errno, fmt, ap);
    va_end(ap);
    abort(); /* dump core and terminate */
    exit(1); /* shouldn't get here */
}
/*
* Nonfatal error unrelated to a system call.
* Print a message and return.
*/
void
err_msg(const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(0, 0, fmt, ap);
    va_end(ap);
}
/*
* Fatal error unrelated to a system call.
* Print a message and terminate.
*/
void
err_quit(const char *fmt, ...)
{
    va_list ap;
    va_start(ap, fmt);
    err_doit(0, 0, fmt, ap);
    va_end(ap);
    exit(1);
}
/*
* Print a message and return to caller.
* Caller specifies "errnoflag".
*/
static void
err_doit(int errnoflag, int error, const char *fmt, va_list ap)
{
    char buf[MAXLINE];
   vsnprintf(buf, MAXLINE, fmt, ap);
   if (errnoflag)
       snprintf(buf+strlen(buf), MAXLINE-strlen(buf), ": %s",
         strerror(error));
   strcat(buf, " ");
   fflush(stdout); /* in case stdout and stderr are the same */
   fputs(buf, stderr);
   fflush(NULL); /* flushes all stdio output streams */
}