[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_t rp,void usrbuf,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_t rp,void usrbuf,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 8192 typedef struct rio_t{ int rio_fd; int rio_cnt; //unread bytes in rio_buf char *rio_bufptr; //next unread byte in rio_buf char rio_buf[RIO_BUFSIZE]; //internal buffer rio_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 -1 ssize_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 -1 ssize_t readlineb(rio_t *rp,void *usrbuf,size_t maxlen); ssize_t readnb(rio_t *rp,void *usrbuf,size_t n); private: //read with buffer ssize_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 empty rp->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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