[Linux] RIO C++封装

RIO包是CSAPP中一个基于read和write函数实现的能够处理终端并提供了带缓冲区读取的IO包。代码很简单，但很巧妙。

缩减了原程序的初始化等函数之后，主要有以下四个对外函数：

1.ssize_t readn(int fd,void *usrbuf,size_t n);

fd为通过open得到的文件描述符，通常为一个小整数。该函数从指定文件读取n个byte到usrbuf中。如果成功执行，返回传输的字节数，如果读到EOF，返回0，如果出错，返回-1。

2.ssize_t writen(int fd,void *usrbuf,size_t n);

该函数将usebuf中最多n个字节写到文件中。如果成功，返回写入的字节数，如果出错返回-1.

3.ssize_t readlineb(rio_trp,voidusrbuf,size_t maxlen);

rio_t是一个定义乐缓冲区的结构体，具体实现见下面代码。该函数一次从缓冲区/文件读取一行数据（最长不超过maxlen)

4.ssize_t readnb(rio_trp,voidusrbuf,size_t n);

该函数是带有缓冲区版本的read，类似于readn。

myrio.h

#pragma once#include <unistd.h>#include <sys/types.h>#include <fcntl.h>#include <errno.h>#include <sys/stat.h>#include <cstring>//a buffer named rio_t#define RIO_BUFSIZE 8192typedef struct rio_t{int rio_fd; int rio_cnt; //unread bytes in rio_bufchar *rio_bufptr; //next unread byte in rio_bufchar rio_buf[RIO_BUFSIZE]; //internal bufferrio_t(int fd):rio_fd(fd),rio_cnt(0),rio_bufptr(rio_buf){ }} rio_t;class Rio{public://io function without internal buffer//Succeed: return the number of byte; EOF: return 0; Fail: return -1ssize_t readn(int fd,void *usrbuf,size_t n);ssize_t writen(int fd,void *usrbuf,size_t n); //io function with internal buffer//Succeed: return the number of byte; EOF: return 0; Fail: return -1ssize_t readlineb(rio_t *rp,void *usrbuf,size_t maxlen);ssize_t readnb(rio_t *rp,void *usrbuf,size_t n);private://read with bufferssize_t rio_read(rio_t *rp,char *usrbuf,size_t n);};

myrio.cpp

#include "myrio.h"//the difference between these function and system's is that://this function can deal with the interrupt. ssize_t Rio::readn(int fd,void *usrbuf,size_t n){size_t nleft = n;ssize_t nread;char *buf = static_cast<char*>(usrbuf);while(nleft > 0){if((nread = read(fd,buf,nleft))<0){if(errno ==EINTR) nread = 0;else return -1;}else if(nleft == 0){break;}else{nleft -= nread;buf += nread;}}return (n - nleft);}ssize_t Rio::writen(int fd,void *usrbuf,size_t n){size_t nleft = n;ssize_t nwriten;char *buf = static_cast<char*>(usrbuf);while(nleft > 0){if((nwriten = write(fd,buf,nleft)) <= 0){if(errno == EINTR) nwriten = 0;else return -1;}else{nleft -= nwriten;buf += nwriten;}return n;}}ssize_t Rio::rio_read(rio_t *rp,char *usrbuf,size_t n){int cnt;while(rp->rio_cnt <= 0){ //refill rio_buf if buf is emptyrp->rio_cnt = read(rp->rio_fd,rp->rio_buf,sizeof(rp->rio_buf)); if(rp->rio_cnt < 0){if(errno != EINTR) return -1;}else if(rp->rio_cnt == 0){return 0;}else{rp->rio_bufptr = rp->rio_buf;}}cnt = n;if(rp->rio_cnt < n)cnt = rp->rio_cnt;memcpy(usrbuf,rp->rio_bufptr,cnt);rp->rio_bufptr += cnt;rp->rio_cnt -= cnt;return cnt;}ssize_t Rio::readlineb(rio_t *rp,void *usrbuf,size_t maxlen){char c;char *buf = static_cast<char*>(usrbuf);int n,rc;for(n=1;n<maxlen;n++){if((rc = rio_read(rp,&c,1)) == 1){*buf = c;buf++;if(c == '\n')break;}else if(rc == 0){if(n == 1) return 0;else break;}else{return -1;}}*buf = '\0';return n;}ssize_t Rio::readnb(rio_t *rp,void *usrbuf,size_t n){size_t nleft = n;ssize_t nread;char *buf = static_cast<char*>(usrbuf);while(nleft > 0){if((nread = rio_read(rp,buf,nleft)) < 0){if(errno == EINTR) nread = 0;else return -1;}else if(nread == 0){break;}else{nleft -= nread;buf += nread;}}return (n-nleft);}

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