ipc/mmap.c

   1 #include <fcntl.h>
   2 #include <stdio.h>
   3 #include <stdlib.h>
   4 #include <string.h>
   5 #include <unistd.h>
   6 #include <sys/mman.h>
   7
   8 /* function prototypes */
   9 void diep(const char *s);
  10
  11 int main(int argc, char *argv[])
  12 {
  13     const char *message = "this shall be written to file\n";
  14     char *map;
  15     int fd;
  16
  17     /* check argument count */
  18     if (argc != 2) {
  19         fprintf(stderr, "Usage: %s\n", argv[0]);
  20         exit(EXIT_FAILURE);
  21     }
  22
  23     /* open file */
  24     if ((fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, (mode_t)0600)) == -1)
  25         diep("open");
  26
  27     /* stretch the file size to the size of the (mmapped) array of chars */
  28     if (lseek(fd, strlen(message) - 1, SEEK_SET) == -1) {
  29         close(fd);
  30         diep("lseek");
  31     }
  32
  33     /* something needs to be written at the end of the file to
  34        have the file actually have the new size */
  35     if (write(fd, "", 1) != 1) {
  36         close(fd);
  37         diep("write");
  38     }
  39
  40     /* mmap() the file */
  41     if ((map = (char *)mmap(0, strlen(message), PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
  42         close(fd);
  43         diep("mmap");
  44     }
  45
  46     /* copy message to mmapped() memory  */
  47     memcpy(map, message, strlen(message));
  48
  49     /* free the mmaped() memory */
  50     if (munmap(map, strlen(message)) == -1) {
  51         close(fd);
  52         exit(EXIT_FAILURE);
  53     }
  54
  55     /* close file */
  56     close(fd);
  57
  58     return EXIT_SUCCESS;
  59 }
  60
  61 void diep(const char *s)
  62 {
  63     perror(s);
  64     exit(EXIT_FAILURE);
  65 }