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struct mq_attr { long mq_flags; /* message queue flag : 0, O_NONBLOCK */ long mq_maxmsg; /* max number of messages allowed on queue*/ long mq_msgsize; /* max size of a message (in bytes)*/ long mq_curmsgs; /* number of messages currently on queue */ }; /* Receive the oldest from highest priority messages in message queue MQDES. */ ssize_t mq_receive (mqd_t __mqdes, char *__msg_ptr, size_t __msg_len, unsigned int *__msg_prio); /* Add message pointed by MSG_PTR to message queue MQDES. */ int mq_send (mqd_t __mqdes, __const char *__msg_ptr, size_t __msg_len, unsigned int __msg_prio);
程序1：向消息队列中发送消息。可指定消息大小及优先级。
// mqsend.c #include "unpipc.h" int main(int argc, char **argv) { mqd_t mqd; void *ptr; size_t len; unsigned int prio; if (argc != 4) err_quit("usage: mqsend <name> <#bytes> <priority>"); len = atoi(argv[2]); prio = atoi(argv[3]); mqd = Mq_open(argv[1], O_WRONLY); ptr = Calloc(len, sizeof(char)); // 使用calloc函数分配一个长度为len的缓冲区，默认被初始化为0 Mq_send(mqd, ptr, len, prio); // 写入消息队列 exit(0); }
程序2：从消息队列读出消息。
// mqreveive.c #include "unpipc.h" int main(int argc, char **argv) { int c, flags; mqd_t mqd; ssize_t n; unsigned int prio; void *buff; struct mq_attr attr; flags = O_RDONLY; while ( (c = Getopt(argc, argv, "n")) != -1) { switch (c) { case ‘n‘: // 命令行中带-n表示以非阻塞模式 flags |= O_NONBLOCK; break; } } if (optind != argc - 1) err_quit("usage: mqreceive [ -n ] <name>"); mqd = Mq_open(argv[optind], flags); Mq_getattr(mqd, &attr); // 这里开辟的缓冲区需要>=消息的最大长度，以便能够容纳接收到的消息 buff = Malloc(attr.mq_msgsize); // 根据最大消息的大小开辟缓冲区以接收消息 n = Mq_receive(mqd, buff, attr.mq_msgsize, &prio); // 这里的len长度需要>=消息的最大长度，否则mq_receive会立即返回EMSGSIZE错误 printf("read %ld bytes, priority = %u\n", (long) n, prio); exit(0); }
运行结果：
[dell@localhost pxmsg]$ ls -l /tmp/mqueue/ 总用量 0 [dell@localhost pxmsg]$ ./mqcreate1 /msgqueue [dell@localhost pxmsg]$ ls -l /tmp/mqueue/ 总用量 0 [dell@localhost pxmsg]$ sudo mount -t mqueue none /tmp/mqueue [sudo] password for dell: [dell@localhost pxmsg]$ ls -l /tmp/mqueue/ 总用量 0 -rw-r--r--. 1 dell dell 80 8月 13 20:52 msgqueue [dell@localhost pxmsg]$ ./mqsend /msgqueue 10 1 [dell@localhost pxmsg]$ ./mqsend /msgqueue 20 2 [dell@localhost pxmsg]$ ./mqsend /msgqueue 30 3 [dell@localhost pxmsg]$ ls -l /tmp/mqueue/ 总用量 0 -rw-r--r--. 1 dell dell 80 8月 13 20:55 msgqueue [dell@localhost pxmsg]$ ./mqreceive /msgqueue read 30 bytes, priority = 3 [dell@localhost pxmsg]$ ./mqreceive /msgqueue read 20 bytes, priority = 2 [dell@localhost pxmsg]$ ./mqreceive /msgqueue read 10 bytes, priority = 1 [dell@localhost pxmsg]$ ./mqreceive /msgqueue ^C [dell@localhost pxmsg]$ ./mqreceive -n /msgqueue mq_receive error: Resource temporarily unavailable [dell@localhost pxmsg]$
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原文地址：http://www.cnblogs.com/fengkang1008/p/4728444.html
