关于:(.text+0x21): undefined reference to `shm_open'问题
2013-11-11 21:36
387 查看
C programming in the UNIX environment的编程手册,一般都会为进程间用共享内存的方法通信提供两组方法:
1. POSIX定义的:
int shm_open(const char *name, int oflag, mode_t mode);
int shm_unlink(const char *name);
int ftruncate(int fd, off_t length);
2. SYSTEM V定义的
int shmget(key_t key, int size, int shmflg);
void *shmat(int shmid, const void *shmaddr, int shmflg);
int shmdt(const void *shmaddr);
int shmctl(int shmid, int cmd, struct shmid_ds *buf);
由于POSIX标准比较通用,一般建议使用该标准定义的方法集。
但是在使用shm_open和shm_unlink两个函数时,你可能遇到和我同样的问题,见如下代码。
该代码旨在测试你的系统是否支持POSIX定义的共享内存函数集。
/* This is just to test if the function is found in the libs. */
#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);
}
假设它所在的文件为"test.c"
我这么编译:
gcc -o test test.c
结果为:
/tmp/ccaGhdRt.o(.text+0x23): In function `main':
: undefined reference to `shm_open'
/tmp/ccaGhdRt.o(.text+0x49): In function `main':
: undefined reference to `shm_unlink'
collect2: ld returned 1 exit status
编译结果实际上是说,没include相应的头文件,或是头文件不存在(即系统不支持该库函数)
但我man shm_open是可以找到帮助文件的(说明系统支持),原因何在???
请注意一下man shm_open的帮助文件的最后几行:
NOTES
These functions are provided in glibc 2.2 and later.
Programs using
these functions must specify the -lrt flag to cc in order to link
against the required ("realtime") library.
POSIX leaves the behavior of the combination of O_RDONLY and O_TRUNC
unspecified. On Linux, this will successfully truncate an existing
shared memory object - this may not be so on other Unices.
The POSIX shared memory object implementation on Linux 2.4 makes use of
a dedicated file system, which is normally mounted under /dev/shm.
如果你注意到的话,这样编译就能通过了:
gcc -lrt -o test test.c
其实就是要连接库的原因。
1. POSIX定义的:
int shm_open(const char *name, int oflag, mode_t mode);
int shm_unlink(const char *name);
int ftruncate(int fd, off_t length);
2. SYSTEM V定义的
int shmget(key_t key, int size, int shmflg);
void *shmat(int shmid, const void *shmaddr, int shmflg);
int shmdt(const void *shmaddr);
int shmctl(int shmid, int cmd, struct shmid_ds *buf);
由于POSIX标准比较通用,一般建议使用该标准定义的方法集。
但是在使用shm_open和shm_unlink两个函数时,你可能遇到和我同样的问题,见如下代码。
该代码旨在测试你的系统是否支持POSIX定义的共享内存函数集。
/* This is just to test if the function is found in the libs. */
#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);
}
假设它所在的文件为"test.c"
我这么编译:
gcc -o test test.c
结果为:
/tmp/ccaGhdRt.o(.text+0x23): In function `main':
: undefined reference to `shm_open'
/tmp/ccaGhdRt.o(.text+0x49): In function `main':
: undefined reference to `shm_unlink'
collect2: ld returned 1 exit status
编译结果实际上是说,没include相应的头文件,或是头文件不存在(即系统不支持该库函数)
但我man shm_open是可以找到帮助文件的(说明系统支持),原因何在???
请注意一下man shm_open的帮助文件的最后几行:
NOTES
These functions are provided in glibc 2.2 and later.
Programs using
these functions must specify the -lrt flag to cc in order to link
against the required ("realtime") library.
POSIX leaves the behavior of the combination of O_RDONLY and O_TRUNC
unspecified. On Linux, this will successfully truncate an existing
shared memory object - this may not be so on other Unices.
The POSIX shared memory object implementation on Linux 2.4 makes use of
a dedicated file system, which is normally mounted under /dev/shm.
如果你注意到的话,这样编译就能通过了:
gcc -lrt -o test test.c
其实就是要连接库的原因。
相关文章推荐
- css+div 小三角tip小提示
- PostgreSQL 源码解读 node的模拟实现
- jQuery中的DOM操作
- Codeforces #211 (Div. 2) B. Fence
- 好难忘又伤心一个非常好的学习js群解散了
- codeforces 363B round211 div2 B. Fence
- [css layout][07] three fixed columns
- 日积月累--小技巧之五
- [css layout][06] three percentage columns
- html5本地存储(Web Storage API)
- javascript设计模式【1】,接口Interface,鸭式辨型
- Reverse Nodes in k-Group
- CSS3+HTML5学习笔记四--CSS三栏布局-宽度只适应
- html display
- CSS水平居中和垂直居中解决方案(转)
- ExtJs中decode与encode
- JS倒计时 代码
- Unix Less Command: 10 Tips for Effective Navigation
- Ping Tutorial: 15 Effective Ping Command Examples
- js 知识总结