未定义的引用“shm_open”，已在此处添加 -lrt 标志

我刚刚遇到系统崩溃并重新安装 Ubuntu 11.10，我的代码产生了这个奇怪的错误。

我写了一个简单的代码示例来测试问题出在哪里：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>

int main (void) {

    int i;

    i = shm_open ("/tmp/shared", O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);   printf ("shm_open rc = %d\n", i);

    shm_unlink ("/tmp/shared");

    return (0);
}

编译命令是

gcc -lrt test.c -o test

错误是：

/tmp/ccxVIUiP.o: In function `main':
test.c:(.text+0x21): undefined reference to `shm_open'
test.c:(.text+0x46): undefined reference to `shm_unlink'
collect2: ld returned 1 exit status

我已经添加了-lrt lib，为什么还是编译不了？

最后的库：

gcc test.c -o 测试 -lrt

From GCC 链接选项 http://gcc.gnu.org/onlinedocs/gcc/Link-Options.html:

-llibrary
-l library
    Search the library named library when linking. 
    (The second alternative with the library as a separate argument
    is only for POSIX compliance and is not recommended.)

    It makes a difference where in the command you write this option;
    the linker searches and processes libraries and object files in the
    order they are specified.
    Thus, `foo.o -lz bar.o' searches library `z' after file foo.o but
    before bar.o. If bar.o refers to functions in `z', those functions
    may not be loaded.