unp daytimetcpcli.c 编译时遇到的一个问题

源码来自：UNP源码
intro目录下的daytimetcpcli.c

在编译时报错：

/tmp/ccB0LkJw.o: In function `main':
daytimetcpcli.c:(.text+0x3d): undefined reference to `err_quit'
daytimetcpcli.c:(.text+0x71): undefined reference to `err_sys'
daytimetcpcli.c:(.text+0xeb): undefined reference to `err_quit'
daytimetcpcli.c:(.text+0x11c): undefined reference to `err_sys'
daytimetcpcli.c:(.text+0x15d): undefined reference to `err_sys'
daytimetcpcli.c:(.text+0x1a2): undefined reference to `err_sys'
collect2: error: ld returned 1 exit status

原因：
没有找到error.c文件

解决：

gcc daytimetcpcli.c ../lib/error.c

加上error.c 后编译可以得到a.out文件