9-23.txt

C++完美演绎 经典算法 如 /* 头文件：my_Include.h */ #include <stdio.h> /* 展开C语言的内建函数指令 */ #define PI 3.141

/* 范例：9-23 */
#include <stdio.h>
#include <stdlib.h>
void main(int argc,char *argv[])
{
  FILE *fp1;
  int pos;

  if((fp1=fopen(argv[1],"w"))==NULL)
  {
    printf("File Open Error!\n");
    exit(1);
  }
  fputs("abcdefg",fp1);
  fputs("\n0123456",fp1);
  fclose(fp1);
  /* 可擦写(更新) */
  if((fp1=fopen(argv[1],"r+"))==NULL)
  {
    printf("文件打开错误\n");
    exit(1);
  }

  pos = fseek(fp1,4,0); 	/* 从文件头跳4bytes */
  putc(65,fp1);
  printf("pos = %d\n",pos);

  fseek(fp1,6,2); 	/* 从文件尾跳6bytes */
  putc('#',fp1);
  fseek(fp1,3,1); 	/* 从目前位置跳3bytes */
  putc('@',fp1);

  fclose(fp1);
}

程序执行结果：(假设输出文件名out)
D:\TC>p9-23 out
pos = 0

D:\TC>type out	=> 检查文件out内容
abcdAfg
0123456      #   @