60 lines
1.2 KiB
C
60 lines
1.2 KiB
C
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/*
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** shmdemo.c -- read and write to a shared memory segment
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/ipc.h>
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#include <sys/shm.h>
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#define SHM_SIZE 1024 /* make it a 1K shared memory segment */
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int main(int argc, char *argv[])
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{
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key_t key;
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int shmid;
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char *data;
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int mode;
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if (argc > 2) {
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fprintf(stderr, "usage: shmdemo [data_to_write]\n");
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exit(1);
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}
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/* make the key: */
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if ((key = ftok("shmdemo.c", 'R')) == -1) {
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perror("ftok");
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exit(1);
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}
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/* connect to (and possibly create) the segment: */
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if ((shmid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) {
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perror("shmget");
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exit(1);
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}
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/* attach to the segment to get a pointer to it: */
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data = shmat(shmid, (void *)0, 0);
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if (data == (char *)(-1)) {
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perror("shmat");
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exit(1);
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}
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/* read or modify the segment, based on the command line: */
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if (argc == 2) {
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printf("writing to segment: \"%s\"\n", argv[1]);
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strncpy(data, argv[1], SHM_SIZE);
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} else
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printf("segment contains: \"%s\"\n", data);
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/* detach from the segment: */
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if (shmdt(data) == -1) {
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perror("shmdt");
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exit(1);
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}
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return 0;
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}
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