3-b.c

来自「Linux下的C代码 实现了对Linux的文件系统的操作」· C语言 代码 · 共 59 行

#include <fcntl.h> 				/* including open() */
#include <sys/stat.h>  			/* including S_IRUSR... */
#include <stdio.h>
#include <stdlib.h>				/* including exit() */
#include <unistd.h>				/* including write, close() */
#include <string.h>

void err_quit(char* msg);

int main(int argc, char** argv)
{
	 int i, len;
	 int fd;
	 char temp[5] = {0, };
	 char *buffer;

	 if ((buffer = (char*)malloc(1024)) == NULL)
		  err_quit("malloc error");
		 
	 memset(buffer, 0, 1024);
	 if ((fd = open("tempfile", O_RDWR | O_TRUNC | O_CREAT, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) < 0)
		  err_quit("open error");
		

	 for (i=1; i<=100; i++)
		  sprintf(buffer+strlen(buffer), "%d", i);  
	 
	 len = strlen(buffer);
	 if (write(fd, buffer, len) != len)
		  err_quit("write error\n");
		 
	 
	 if (lseek(fd, 50, SEEK_SET) < 0)
		  err_quit("lseek error\n");
	 if (read(fd, temp, 1) != 1)
		  err_quit("read error");
	 printf("The 50th byte is: %s\n", temp);

	 if (lseek(fd, 100, SEEK_SET) < 0 )
		  err_quit("lseek error\n");
	 if (read(fd, temp, 1) != 1)
		  err_quit("read error");
	 printf("The 100th byte is: %s\n", temp);
		  
	 close(fd);

	 if (unlink("tempfile") < 0)
		  err_quit("unlink error");
	 
	 return 0;
		  
}

void err_quit(char* msg)
{
	 fprintf(stderr, msg);
	 exit(1);
}