[ Linux ] 缓冲区的理解 以及简易模拟实现封装C标准库

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

int main()
{
printf("hello printf");// stdout -> 1
const char* msg = "hello write";
write(1,msg,strlen(msg));
sleep(5);
return 0;
}

//在/usr/include/libio.h
struct _IO_FILE
{
int _flags; /* High-order word is _IO_MAGIC; rest is flags. */
#define _IO_file_flags _flags
//缓冲区相关
/* The following pointers correspond to the C++ streambuf protocol. */
/* Note: Tk uses the _IO_read_ptr and _IO_read_end fields directly. */
char *_IO_read_ptr; /* Current read pointer */
char *_IO_read_end; /* End of get area. */
char *_IO_read_base; /* Start of putback+get area. */
char *_IO_write_base; /* Start of put area. */
char *_IO_write_ptr; /* Current put pointer. */
char *_IO_write_end; /* End of put area. */
char *_IO_buf_base; /* Start of reserve area. */
char *_IO_buf_end; /* End of reserve area. */
/* The following fields are used to support backing up and undo. */
char *_IO_save_base; /* Pointer to start of non-current get area. */
char *_IO_backup_base; /* Pointer to first valid character of backup area */
char *_IO_save_end; /* Pointer to end of non-current get area. */
struct _IO_marker *_markers;
struct _IO_FILE *_chain;
int _fileno; //封装的文件描述符
#if 0
int _blksize;
#else
int _flags2;
#endif
_IO_off_t _old_offset; /* This used to be _offset but it's too small. */
#define __HAVE_COLUMN /* temporary */
/* 1+column number of pbase(); 0 is unknown. */
unsigned short _cur_column;
signed char _vtable_offset;
char _shortbuf[1];
/* char* _save_gptr; char* _save_egptr; */
_IO_lock_t *_lock;
#ifdef _IO_USE_OLD_IO_FILE
};

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

int main()
{
const char *str1 = "hello printf\n";
const char *str2 = "hello fprintf\n";
const char *str3 = "hello fputs\n";
const char *str4 = "hello write\n";

//C库函数
printf(str1);
fprintf(stdout,str2);
fputs(str3,stdout);

//系统接口
write(1,str4,strlen(str4));

//是调用完了上面的代码才执行的fork
fork();

return 0;
}

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

#define NUM 1024

#define NONE_FLUSH 0x0
#define LINE_FLUSH 0x1
#define FULL_FLUSH 0x2

typedef struct _MyFILE
{
int _fileno;
char _buffer[NUM];
int _end;
int _flags;//fflush method
}MyFILE;

MyFILE *my_fopen(const char* filename,const char*method)
{
assert(filename);
assert(method);

int flags = O_RDONLY;

if(strcmp(method,"r") == 0)
{
}
else if(strcmp(method,"r+") == 0)
{}
else if(strcmp(method,"w") == 0)
{
flags = O_WRONLY | O_CREAT |O_TRUNC;
}
else if(strcmp(method,"w+") == 0)
{}
else if(strcmp(method,"a") == 0)
{
flags = O_WRONLY | O_CREAT |O_APPEND;
}
else if(strcmp(method,"a+") == 0)
{}

int fileno = open(filename,flags,0666);
if(fileno < 0)
{
return NULL;
}

MyFILE *fp = (MyFILE*)malloc(sizeof(MyFILE));
if(fp == NULL ) return fp;
memset(fp,0,sizeof(MyFILE));

fp->_fileno = fileno;
fp->_flags |= LINE_FLUSH;
fp->_end = 0;
return fp;
}
void my_fflush(MyFILE* fp)
{
assert(fp);
if(fp->_end > 0)
{
write(fp->_fileno,fp->_buffer,fp->_end);
fp->_end =0;
syncfs(fp->_fileno);
}

}

void my_fwrite(MyFILE* fp,const char* start,int len)
{
assert(fp);
assert(start);
assert(len>0);

// abcde->追加
strncpy(fp->_buffer+fp->_end,start,len);//将数据写入缓冲区
fp->_end += len;

if(fp->_flags & NONE_FLUSH){}
if(fp->_flags & LINE_FLUSH)
{
if(fp->_end > 0 && fp->_buffer[fp->_end-1] == '\n')
{
write(fp->_fileno,fp->_buffer,fp->_end);
fp->_end = 0;
syncfs(fp->_fileno);
}
}
if(fp->_flags & FULL_FLUSH){}

}

void my_fclose(MyFILE* fp)
{
my_fflush(fp);
close(fp->_fileno);
free(fp);
}

int main()
{
MyFILE * fp = my_fopen("log.txt","w");
if(fp == NULL)
{
printf("my_fopen error\n");
return 1;
}
const char *msg = "hello my_file 11111111\n";
my_fwrite(fp,msg,strlen(msg));

printf("hello my_file 11111111消息立即刷新\n");
sleep(3);


const char *mssg = "hello 222222222";
my_fwrite(fp,mssg,strlen(mssg));
sleep(3);
printf("写入了一个不满足条件的字符串hello 222222222\n");

const char *msssg = "hello 33333333";
my_fwrite(fp,msssg,strlen(msssg));
sleep(3);
printf("写入了一个不满足条件的字符串hello 33333333\n");

const char *mssssg = "end\n";
my_fwrite(fp,mssssg,strlen(mssssg));
printf("写了一个满足条件的字符串end\n");
sleep(3);


const char *msssssg = "aaaaaaa";
my_fwrite(fp,msssssg,strlen(msssssg));
printf("写了一个满足条件的字符串aaaaaaa\n");
sleep(1);
my_fflush(fp);
sleep(3);

my_fclose(fp);
return 0;
}