深究标准IO的缓存

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(void)
{
  char buf[5];
  FILE *myfile = stdin;
  fgets(buf,,myfile);
  fputs(buf,myfile);
  
  return 0;
}

struct _IO_FILE {
int _flags;
#define _IO_file_flags _flags



char* _IO_read_ptr;
 _IO_read_end;
 _IO_read_base;
 _IO_write_base;
 _IO_write_ptr;
 _IO_write_end;
 _IO_buf_base;
 _IO_buf_end;

char *_IO_save_base;
_IO_backup_base;
_IO_save_end;

struct _IO_marker *_markers;

struct _IO_FILE *_chain;

 _fileno;
};

1.
 _IO_read_base;
2 _IO_write_end;
3char* _IO_buf_end;

#include <stdlib.h>stdin;
  printf("before reading/n");
  printf(read buffer base %p/n",myfile->_IO_read_base);
  printf(read buffer length %d/nwrite buffer base %p/n_IO_write_base);
  printf(write buffer length %d/nbuf buffer base %p/n_IO_buf_base);
  printf(buf buffer length %d/n/n);
  fgets(buf,myfile);
  printf(after reading/n_IO_buf_base);

  ;
}

#include <stdlib.h>];
  cur;
  FILE *myfile;
  myfile = fopen(bbb.txtrbefore reading,myfile->_IO_read_ptr: %d/n_IO_read_base);
  fgets(buf,1)">5,myfile); //仅仅读4个字符
  cur = myfile->_IO_read_base;
  while (cur <</span> myfile->_IO_read_end) 实际上读满了这个缓冲区
  {
    printf(%ccur);
    cur++;
  }
  printf(/nafter reading,1)">_IO_read_base);
  ;
}

#include <stdlib.h>2048]={};
   i;
  FILE *aaa.txtr+);
  i= ;
  while (i<</span>2048)
  {
    fwrite(buf+i,1)">1,1)">512;
    注释掉这句则可以写入aaa.txt
    myfile->_IO_write_ptr = myfile->_IO_write_base;
    printf(%p write buffer base/n_IO_write_base);
    printf(%p buf buffer base /n_IO_buf_base);
    printf(%p read buffer base /n_IO_read_base);
    printf(%p write buffer ptr /n_IO_write_ptr);
    printf();
  }
  ;
}

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

char buf2[10];
  
  fgets(buf,stdin); 第一次输入时,超过5个字符

  puts(stdin->_IO_read_ptr);本句说明整行会被一次全部读入缓冲区,而非仅仅上面需要的个字符
  stdin->_IO_read_ptr = stdin->_IO_read_end; 标准I/O会认为缓冲区已空,再次调用read
                                             注释掉,再看看效果
  printf();
  puts(buf);
  
  fgets(buf2,stdin);
  puts(buf2);
  
  ;
}

#include <stdlib.h>5]={'1',1)">2345'}; 最后一个不要是/n,是/n的话,标准I/O会自动flush的
                                                    这是行缓冲跟全缓冲的重要区别

void writeLog(FILE *ftmp)
{
  fprintf(ftmp,stdout->_IO_write_base);
  fprintf(ftmp,1)">_IO_buf_base);
  fprintf(ftmp,1)">_IO_read_base);
  fprintf(ftmp,1)">_IO_write_ptr);
  fprintf(ftmp,1)">);
}

ftmp;
  ftmp = fopen(ccc.txtw4)
  {
    fwrite(buf,stdout);
    i++;
    *stdout->_IO_write_ptr++ = ';可以单独把这句打开,看看效果
    getchar();getchar()会标准I/O将缓冲区输出
    打开下面的注释,你就会发现屏幕上什么输出也没有
    stdout->_IO_write_ptr = stdout->_IO_write_base;
    writeLog(ftmp); 这个只是为了查看缓冲区指针的变化  
  }
  ;
}

#include <</span>stdlib.h>
#include <</span>stdio.h>
#include <</span>sys/types.h>
#include <</span>sys/stat.h>
#include <</span>fcntl.h>

)
{
  fputs(stderr%d/n;
}

#include <stdlib.h>];

  fgets(buf,1)">sizeof(buf),stdin);输入要于4个,少于13个字符才能看出效果
  puts(buf);

  交替注释下面两行
  stdin->_IO_read_end = stdin->_IO_read_ptr+1;

  stdin->_IO_read_end = stdin->_IO_read_ptr + sizeof(buf2)-;
   
  fgets(buf2,1)">sizeof(buf2),stdin);
  puts(buf2);
  if (feof(stdin))
    printf(input end/n);
  ;
}