Question

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所在：

#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);
}

并且编译命令是

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，为什么它仍然没有编译？

Answer 1

最后的图书馆：

gcc test.c -o test -lrt

来自GCC Link Options：

-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.

Answer 2

从

更改编译行

gcc -lrt test.c -o test

到

gcc test.c -o test -lrt

Answer 3

在Expert C programming页面108： <Handy Heuristic> Where to Put Library Options:Always put the -l library options at the rightmost end of your compilation command line. 但它没有说明原因，所以我想这有点规律？：）

Answer 4

对于像我一样使用超级自动魔法 CMAKE 的人，请尝试添加：

target_link_libraries(your_binary_name PRIVATE librt.so)

到您的CMakeLists.txt

或者，根据需要将 PRIVATE 替换为 PUBLIC..

如果您已经建立了良好的库路径（例如，/usr/lib 中所有需要的库），您可能只需在 CMakeLists.txt 中声明即可：

set(CMAKE_CXX_FLAGS "-lrt")

未定义的引用＆＃39; shm_open＆＃39;，已在此处添加-lrt标志

4 个答案: