mqopen 出错！！

[ShowMan]

#include <stdio.h>
#include <math.h>
#include <mqueue.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#define PMODE 0666

int main()
{
int i;
mqd_t mqfd;
struct mq_attr attr;
int open_flags = 0;

attr.mq_maxmsg = 20;
attr.mq_msgsize = 30;
attr.mq_flags = 0;
open_flags = O_CREAT;
mqfd = mq_open("queuemsg",open_flags,PMODE,NULL);
if (mqfd ==(mqd_t)-1)
{
perror("mq_open failure from main");
exit(0);
};
mq_close(mqfd);
printf("success");
}
编译执行
mq_open failure from main: Invalid argument

出错了，请问mq_open 如何使用才是正确的

[mymtom]

根据http://www.opengroup.org/onlinepubs/009695399/functions/mq_open.html的描述：

If name begins with the slash character, then processes calling mq_open() with the same value of name shall refer to the same message queue object, as long as that name has not been removed. If name does not begin with the slash character, the effect is implementation-defined. The interpretation of slash characters other than the leading slash character in name is implementation-defined. If the name argument is not the name of an existing message queue and creation is not requested, mq_open() shall fail and return an error.

建议 name 参数以一个斜杠"/"开头，而且只有一个斜杠。

#include <stdio.h>
#include <string.h>

#include <limits.h>
#include <fcntl.h>
#include <sys/stat.h>

#include <mqueue.h>

#define FILE_MODE (S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH)

int main(void)
{
        mqd_t mqd;
        int oflag;
        char name[PATH_MAX + 1];

        oflag = O_CREAT | O_RDWR;
        strcpy(name, "/mq_mymtom");
        mqd = mq_open(name, oflag, FILE_MODE, NULL);
        if ((mqd_t)-1 == mqd)
                perror("mq_open()");
        else
                printf("mq_open(): success.\n");

        strcpy(name, "mq_mymtom");
        mqd = mq_open(name, oflag, FILE_MODE, NULL);
        if ((mqd_t)-1 == mqd)
                perror("mq_open()");
        else
                printf("mq_open(): success.\n");

        return 0;
}