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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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* 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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