The Linux Programming Interface: a linux and unix system Programming Handbook
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| Listing 46-3: Using
msgrcv() to read a message ––––––––––––––––––––––––––––––––––––––––––––––––––––– svmsg/svmsg_receive.c #define _GNU_SOURCE /* Get definition of MSG_EXCEPT */ #include #include #include "tlpi_hdr.h" #define MAX_MTEXT 1024 struct mbuf { long mtype; /* Message type */ char mtext[MAX_MTEXT]; /* Message body */ }; static void usageError(const char *progName, const char *msg) { if (msg != NULL) fprintf(stderr, "%s", msg); fprintf(stderr, "Usage: %s [options] msqid [max-bytes]\n", progName); fprintf(stderr, "Permitted options are:\n"); fprintf(stderr, " -e Use MSG_NOERROR flag\n"); fprintf(stderr, " -t type Select message of given type\n"); fprintf(stderr, " -n Use IPC_NOWAIT flag\n"); 946 Chapter 46 #ifdef MSG_EXCEPT fprintf(stderr, " -x Use MSG_EXCEPT flag\n"); #endif exit(EXIT_FAILURE); } int main(int argc, char *argv[]) { int msqid, flags, type; ssize_t msgLen; size_t maxBytes; struct mbuf msg; /* Message buffer for msgrcv() */ int opt; /* Option character from getopt() */ /* Parse command-line options and arguments */ flags = 0; type = 0; while ((opt = getopt(argc, argv, "ent:x")) != -1) { switch (opt) { case 'e': flags |= MSG_NOERROR; break; case 'n': flags |= IPC_NOWAIT; break; case 't': type = atoi(optarg); break; #ifdef MSG_EXCEPT case 'x': flags |= MSG_EXCEPT; break; #endif default: usageError(argv[0], NULL); } } if (argc < optind + 1 || argc > optind + 2) usageError(argv[0], "Wrong number of arguments\n"); msqid = getInt(argv[optind], 0, "msqid"); maxBytes = (argc > optind + 1) ? getInt(argv[optind + 1], 0, "max-bytes") : MAX_MTEXT; /* Get message and display on stdout */ msgLen = msgrcv(msqid, &msg, maxBytes, type, flags); if (msgLen == -1) errExit("msgrcv"); printf("Received: type=%ld; length=%ld", msg.mtype, (long) msgLen); if (msgLen > 0) printf("; body=%s", msg.mtext); printf("\n"); exit(EXIT_SUCCESS); } ––––––––––––––––––––––––––––––––––––––––––––––––––––– tải về 6.93 Mb. Chia sẻ với bạn bè của bạn:
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