pshm/pshm_write.c

This is pshm/pshm_write.c (Listing 54-2, page 1112), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* pshm_write.c

   Usage: pshm_write shm-name string

   Copy 'string' into the POSIX shared memory object named in 'shm-name'.

   See also pshm_read.c.
*/
#include <fcntl.h>
#include <sys/mman.h>
#include "tlpi_hdr.h"
int
main(int argc, char *argv[])
{
    int fd;
    size_t len;                 /* Size of shared memory object */
    char *addr;

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s shm-name string\n", argv[0]);

    fd = shm_open(argv[1], O_RDWR, 0);      /* Open existing object */
    if (fd == -1)
        errExit("shm_open");

    len = strlen(argv[2]);
    if (ftruncate(fd, len) == -1)           /* Resize object to hold string */
        errExit("ftruncate");
    printf("Resized to %ld bytes\n", (long) len);

    addr = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED)
        errExit("mmap");

    if (close(fd) == -1)                    /* 'fd' is no longer needed */
        errExit("close");

    printf("copying %ld bytes\n", (long) len);
    memcpy(addr, argv[2], len);             /* Copy string to shared memory */
    exit(EXIT_SUCCESS);
}

 

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