write.c

这个是学习嵌入式开发的重要例子

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/mman.h>
#include <fcntl.h>

#define BUFFER_SIZE	32

typedef struct _human
{
  unsigned long id;
  unsigned long weight;
  unsigned long length;
  unsigned long married;
  char name[BUFFER_SIZE];
} human_t;

int main(int argc, char **argv)
{
  int fd;

  if (argc < 2)
  {
    fprintf(stdout, "Usage: %s <filename>\n", argv[0]);
    exit(1);
  }

  if ((fd = open(argv[1], O_RDWR | O_CREAT | O_EXCL, 0644)) < 0)
  {
    if (errno != EEXIST)
    {
      fprintf(stderr, "open() failed: %s", strerror(errno));
      exit(1);
    }
    else
    {
      if ((fd = open(argv[1], O_RDWR)) < 0)
      {
	fprintf(stderr, "open() failed: %s", strerror(errno));
	exit(1);
      }
    }
  }

  lseek(fd, 30 * sizeof(human_t), SEEK_SET);
  write(fd, "", 1);

  human_t *h;

  if ((h = mmap(NULL, 30 * sizeof(human_t), PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED)
  {
    fprintf(stderr, "mmap() failed: %s\n", strerror(errno));
    exit(1);
  }

  fprintf(stdout, "mmap() successed.\n");

  close(fd);
  fprintf(stdout, "closed file.\n");

  int i;

  for (i = 0; i < 30; i++)
  {
    (h + i)->id = i;
    (h + i)->weight = 80 + i;
    (h + i)->length = 180 + i;
    //memcpy((h + i)->name, "Ligen", strlen("Ligen"));
    snprintf((h + i)->name, BUFFER_SIZE, "Ligen %d", i);
    (h + i)->married = 0;
  }

  fprintf(stdout, "write infomation to mapped area.\n");

  for (;;)
  {
  }

  return 0;
}