system call test

Posted 2021-06-17 jingmojing

1

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
  int fd = -1;
  int ret = 1;
  int buffer = 1024;
  int num = 0;

  // O_CREAT: 当文件不存在时，创建一个新文件；O_RDWR: 以读写方式打开；O_TRUNC: 打开文件后，将文件的长度截断为0
  if((fd=open("./test", O_RDWR|O_CREAT|O_TRUNC))==-1)
  {
    printf("Open Error\\n");
    exit(1);
  }

  ret = write(fd, &buffer, sizeof(int));
  if( ret < 0)
  {
    printf("write Error\\n");
    exit(1);
  }
  printf("write %d byte(s)\\n",ret);

  lseek(fd, 0L, SEEK_SET);
  ret= read(fd, &num, sizeof(int));
  if(ret==-1)
  {
    printf("read Error\\n");
    exit(1);
  }
  printf("read %d byte(s)，the number is %d\\n", ret, num);

  close(fd);

  return 0;
}