浅谈无缓存I/O操作和标准I/O文件操作区别 浅谈生物课程标准

#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, 5, myfile);
fputs(buf, myfile);

return 0;
}

struct _IO_FILE {
int _flags;
#define _IO_file_flags _flags



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

char *_IO_save_base;
char *_IO_backup_base;
char *_IO_save_end;

struct _IO_marker*_markers;

struct _IO_FILE*_chain;

int _fileno;
};

#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;
printf("before readingn");
printf("read buffer base%pn",myfile->_IO_read_base);
printf("read buffer length%dn",myfile->_IO_read_end- myfile->_IO_read_base);
printf("write buffer base%pn",myfile->_IO_write_base);
printf("write buffer length%dn",myfile->_IO_write_end- myfile->_IO_write_base);
printf("buf buffer base%pn",myfile->_IO_buf_base);
printf("buf buffer length%dn",myfile->_IO_buf_end- myfile->_IO_buf_base);
printf("n");
fgets(buf, 5, myfile);
fputs(buf, myfile);
printf("n");
printf("after readingn");
printf("read buffer base%pn",myfile->_IO_read_base);
printf("read buffer length%dn",myfile->_IO_read_end- myfile->_IO_read_base);
printf("write buffer base%pn",myfile->_IO_write_base);
printf("write buffer length%dn",myfile->_IO_write_end- myfile->_IO_write_base);
printf("buf buffer base%pn",myfile->_IO_buf_base);
printf("buf buffer length%dn",myfile->_IO_buf_end- myfile->_IO_buf_base);

return 0;
}

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

int main(void)
{
char buf[5];
char *cur;
FILE *myfile;
myfile = fopen("bbb.txt", "r");
printf("before reading,myfile->_IO_read_ptr: %dn", myfile->_IO_read_ptr- myfile->_IO_read_base);
fgets(buf, 5, myfile); //仅仅读4个字符
cur = myfile->_IO_read_base;
while (cur < myfile->_IO_read_end)//实际上读满了这个缓冲区
{
printf("%c",*cur);
cur++;
}
printf("nafter reading,myfile->_IO_read_ptr: %dn", myfile->_IO_read_ptr- myfile->_IO_read_base);
return 0;
}

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


int main(void)
{
char buf[2048]={0};
int i;
FILE *myfile;
myfile = fopen("aaa.txt", "r+");
i= 0;
while (i<2048)
{
fwrite(buf+i,1, 512, myfile);
i+=512;
//注释掉这句则可以写入aaa.txt
myfile->_IO_write_ptr= myfile->_IO_write_base;
printf("%pwrite buffer basen", myfile->_IO_write_base);
printf("%pbuf buffer base n", myfile->_IO_buf_base);
printf("%pread buffer base n", myfile->_IO_read_base);
printf("%pwrite buffer ptr n", myfile->_IO_write_ptr);
printf("n");
}
return 0;
}

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

int main(void)
{
char buf[5];
char buf2[10];

fgets(buf, 5, 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("n");
puts(buf);

fgets(buf2, 10, stdin);
puts(buf2);

return 0;
}

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

char buf[5]={'1','2', '3', '4', '5'}; //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

voidwriteLog(FILE *ftmp)
{
fprintf(ftmp, "%p write bufferbasen",stdout->_IO_write_base);
fprintf(ftmp, "%p buf buffer basen",stdout->_IO_buf_base);
fprintf(ftmp, "%p read buffer basen",stdout->_IO_read_base);
fprintf(ftmp, "%p write buffer ptrn",stdout->_IO_write_ptr);
fprintf(ftmp, "n");
}

int main(void)
{
int i;
FILE *ftmp;
ftmp = fopen("ccc.txt", "w");
i= 0;
while (i<4)
{
fwrite(buf,1, 5, stdout);
i++;
*stdout->_IO_write_ptr++= 'n';//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
}
return 0;
}

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

int main(void)
{
fputs("stderr", stderr);
printf("%dn", stderr->_IO_buf_end- stderr->_IO_buf_base);

return 0;
}

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

int main(void)
{
char buf[5];
char buf2[10];

fgets(buf, 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)-1;

fgets(buf2, sizeof(buf2), stdin);
puts(buf2);
if (feof(stdin))
printf("inputendn");
return 0;
}