[Muduo网络库源码分析] (5) base/FileUtil.cc_h_文件操作

文件操作

实现：ReadSmallFile、AppendFile类

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功能：实现文件内容、信息的读取与写入

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知识点：

• fwrite_unlocked
  fwrite 和 fwrite_unlocked是一对，其中fwrite_unlocked是fwrite的线程不安全版本，因为不加锁。

• O_CLOEXEC
  调用open函数O_CLOEXEC模式打开的文件描述符在执行exec调用新程序中关闭，且为原子操作

• pread()
  //pread() reads up to count bytes from file descriptor fd at offset offset (from the start of the file) into the buffer starting at buf. The file offset is not changed.

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用途：

可用于文件读取与写入，可用于日志的写入

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模块拆分与封装：

已把其文件读取模块单独分离出来，并利用Makefile统一编译，模块代码地址如下：https://github.com/chudongfang/Learn_From_Muduo/tree/master/FileRead

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代码及分析：

FileUtil.cc

// Copyright 2010, Shuo Chen.  All rights reserved.// http://code.google.com/p/muduo///// Use of this source code is governed by a BSD-style license// that can be found in the License file.// Author: Shuo Chen (chenshuo at chenshuo dot com)//#include <muduo/base/FileUtil.h>#include <muduo/base/Logging.h> // strerror_tl#include <boost/static_assert.hpp>#include <assert.h>#include <errno.h>#include <fcntl.h>#include <stdio.h>#include <sys/stat.h>using namespace muduo;//构造函数FileUtil::AppendFile::AppendFile(StringArg filename)  : fp_(::fopen(filename.c_str(), "ae")),  // 'e' for O_CLOEXEC    writtenBytes_(0){  assert(fp_);  //设置缓冲区  ::setbuffer(fp_, buffer_, sizeof buffer_);  // posix_fadvise POSIX_FADV_DONTNEED ?}//析构函数FileUtil::AppendFile::~AppendFile(){  //关闭文件  ::fclose(fp_);}//向文件中写长度len的loglinevoid FileUtil::AppendFile::append(const char* logline, const size_t len){  //写入文件  size_t n = write(logline, len);  size_t remain = len - n;  while (remain > 0)  {    size_t x = write(logline + n, remain);    //如果写入失败，报错    if (x == 0)    {      int err = ferror(fp_);      if (err)      {        fprintf(stderr, "AppendFile::append() failed %s\n", strerror_tl(err));      }      break;    }    //n代表已经写入的数    n += x;    //remain代表还需写入的数    remain = len - n; // remain -= x  }  //已经写入文件的总字节数  writtenBytes_ += len;}//刷新文件流void FileUtil::AppendFile::flush(){  ::fflush(fp_);}size_t FileUtil::AppendFile::write(const char* logline, size_t len){  // #undef fwrite_unlocked  //写文件的不加锁的版本，线程不安全  return ::fwrite_unlocked(logline, 1, len, fp_);}//读文件构造函数，在此期间打开文件，并记录文件描述符//调用open函数O_CLOEXEC模式打开的文件描述符在执行exec调用新程序中关闭，且为原子操作FileUtil::ReadSmallFile::ReadSmallFile(StringArg filename)  : fd_(::open(filename.c_str(), O_RDONLY | O_CLOEXEC)),    err_(0){  //清空缓冲区  buf_[0] = '\0';  if (fd_ < 0)  {    err_ = errno;  }}//析构函数，关闭文件描述符FileUtil::ReadSmallFile::~ReadSmallFile(){  if (fd_ >= 0)  {    ::close(fd_); // FIXME: check EINTR  }}// return errno// 获取文件信息，并把文件内容读入到content中template<typename String>int FileUtil::ReadSmallFile::readToString(int maxSize,                                          String* content,                                          int64_t* fileSize,                                          int64_t* modifyTime,                                          int64_t* createTime){  //编译期间断言  long int 是否占八位  BOOST_STATIC_ASSERT(sizeof(off_t) == 8);  assert(content != NULL);  int err = err_;  if (fd_ >= 0)  {     //清空    content->clear();    if (fileSize)    {      //获取文件信息到statbut      struct stat statbuf;      if (::fstat(fd_, &statbuf) == 0)      {        //是否是常规文件        if (S_ISREG(statbuf.st_mode))        {          *fileSize = statbuf.st_size;          //申请空间          content->reserve(static_cast<int>(std::min(implicit_cast<int64_t>(maxSize), *fileSize)));        }        //是否是一个目录        else if (S_ISDIR(statbuf.st_mode))        {          err = EISDIR;        }        //或取文件内容最后被修改的时间        if (modifyTime)        {          *modifyTime = statbuf.st_mtime;        }        //获取文件状态（属性）改变时间        if (createTime)        {          *createTime = statbuf.st_ctime;        }      }      else      {        err = errno;      }    }    while (content->size() < implicit_cast<size_t>(maxSize))    {      //确定要读的字节数      size_t toRead = std::min(implicit_cast<size_t>(maxSize) - content->size(), sizeof(buf_));      //long      ssize_t n = ::read(fd_, buf_, toRead);      if (n > 0)      {        content->append(buf_, n);      }      else      {        if (n < 0)        {          err = errno;        }        break;      }    }  }  return err;}//把文件中的内容读进缓冲区，并给size赋值为文件的大小int FileUtil::ReadSmallFile::readToBuffer(int* size){  int err = err_;  if (fd_ >= 0)  {    //pread()  reads  up to count bytes from file descriptor fd at offset offset (from the start of the    //file) into the buffer starting at buf.  The file offset is not changed.    ssize_t n = ::pread(fd_, buf_, sizeof(buf_)-1, 0);    if (n >= 0)    {      if (size)      {        *size = static_cast<int>(n);      }      buf_[n] = '\0';    }    else    {      err = errno;    }  }  return err;}template int FileUtil::readFile(StringArg filename,                                int maxSize,                                string* content,                                int64_t*, int64_t*, int64_t*);template int FileUtil::ReadSmallFile::readToString(    int maxSize,    string* content,    int64_t*, int64_t*, int64_t*);#ifndef MUDUO_STD_STRINGtemplate int FileUtil::readFile(StringArg filename,                                int maxSize,                                std::string* content,                                int64_t*, int64_t*, int64_t*);template int FileUtil::ReadSmallFile::readToString(    int maxSize,    std::string* content,    int64_t*, int64_t*, int64_t*);#endif

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FileUtil.h

// Copyright 2010, Shuo Chen.  All rights reserved.// http://code.google.com/p/muduo///// Use of this source code is governed by a BSD-style license// that can be found in the License file.// Author: Shuo Chen (chenshuo at chenshuo dot com)//// This is a public header file, it must only include public header files.#ifndef MUDUO_BASE_FILEUTIL_H#define MUDUO_BASE_FILEUTIL_H#include <muduo/base/StringPiece.h>#include <boost/noncopyable.hpp>namespace muduo{namespace FileUtil{//用来读取小文件// read small file < 64KBclass ReadSmallFile : boost::noncopyable{ public:  //构造函数  ReadSmallFile(StringArg filename);  ~ReadSmallFile();  // return errno  //读文件到缓冲区，并获取文件信息  template<typename String>  int readToString(int maxSize,                   String* content,                   int64_t* fileSize,                   int64_t* modifyTime,                   int64_t* createTime);  /// Read at maxium kBufferSize into buf_  // return errno  //读文件到缓冲区，并将size值置为文件大小  int readToBuffer(int* size);  //返回缓冲区指针，不能通过其对数据进行修改  const char* buffer() const { return buf_; }  //设置缓冲区大小  static const int kBufferSize = 64*1024; private:  //文件描述符  int fd_;  int err_;  //缓冲区  char buf_[kBufferSize];};//读文件内容，并且获取文件信息// read the file content, returns errno if error happens.template<typename String>int readFile(StringArg filename,             int maxSize,             String* content,             int64_t* fileSize = NULL,             int64_t* modifyTime = NULL,             int64_t* createTime = NULL){  ReadSmallFile file(filename);  return file.readToString(maxSize, content, fileSize, modifyTime, createTime);}//// not thread safeclass AppendFile : boost::noncopyable{ public:  explicit AppendFile(StringArg filename);  ~AppendFile();  //向文件追加长度n的logline  void append(const char* logline, const size_t len);  //清空文件流  void flush();  //返回已经写入的字节数   size_t writtenBytes() const { return writtenBytes_; } private:  //线程不安全的写文件函数  size_t write(const char* logline, size_t len);  FILE* fp_;//文件结构体  //缓冲区  char buffer_[64*1024];  //写入的数据量  size_t writtenBytes_;};}}#endif  // MUDUO_BASE_FILEUTIL_H