标签：targe 成员变量 return 信息 生成 assert https 时间 +=
所有的商业软件或线上系统都具有日志功能，因为日志信息提供了系统启动以来的重要的操作或状态迁移记录，是追踪各种异常错误的第一手资料。绝大部分系统的日志模块会自动保留历史日志文件，即：日志文件大小达到约定上限时，自动转储到一个新的历史文件，当前文件清空并继续记录新的日志信息，例如：假设当前日志文件名为test.log, 当它的大小到达上限（例如10MB)时，就把其文件内容转储到新文件test.log.1, 然后test.log清空并继续记录新信息。根据配置不同，我们可以保留1到N份历史日志文件。当历史日志文件数目达到上限时，我们可以采用round-robin策略（或其他策略）依据文件生成时间依次覆盖老的文件。本文尝试用C++实现上述日志文件功能，其功能归纳总结如下：
1） 日志文件提供接口让用户配置日志文件名、日志大小上限、历史日志文件数目上限；
2） 日志文件提供Append()接口，让用户向文件追加日志消息；
3） 日志文件在执行Append()接口过程中，自动检测当前日志文件大小：如果追加当前消息后，文件大小超过约定上限，则记录当前消息前，将已有消息转储到历史文件并保证历史日志文件数不超过约定上限；否者，直接记录当前消息；
4） 日志文件提供接口让用户配置是否对历史日志文件进行压缩;
LogFile类实现了上述功能，先看一下其接口定义：
1 #ifndef _LOGFILE_H 2 #define _LOGFILE_H 3 4 #include <fstream> 5 #include <iostream> 6 7 8 class LogFile { 9 public: 10 LogFile(const LogFile &) = delete; 11 LogFile& operator=(const LogFile &) = delete; 12 LogFile(const std::string&, double, unsigned int); 13 14 ~LogFile(); 15 void Append(std::string &&msg); 16 17 private: 18 void Rotate(); 19 double GetFileSize(); 20 std::string NextHistoryFile(); 21 22 private: 23 std::ofstream ofs_; 24 std::string file_name_; 25 double cur_size_; 26 double max_size_; 27 unsigned int max_file_num_; 28 }; 29 30 #endif //_LOGFILE_H
ofs_: c++ std::ofstream类型对象，通过其操作符"<<"把消息写入日志文件
file_name_: 日志文件名；
cur_size_: 实时记录当前日志文件大小，避免每次执行Append()操作时调用系统函数获取文件大小；
max_size_: 用户指定的日志文件上限；
max_file_num_: 用户指定的最大历史文件数；
LogFile(const std::string&, double, unsigned int): LogFile类的唯一构造函数，可以指定日志文件名，文件大小上限，历史文件数量上限，其实现也非常简单：
LogFile::LogFile(const std::string& file_name, double max_size, unsigned int max_file_num) : file_name_(file_name), max_size_(max_size), max_file_num_(max_file_num) { assert(max_file_num_ > 0); cur_size_ = GetFileSize(); ofs_.open(file_name_, std::ofstream::out|std::ofstream::app); }
~LogFile()： 析构函数，主要功能是关闭在构造函数中打开的ofstream对象.
LogFile::~LogFile() { if (ofs_.is_open()) { ofs_.close(); } }
void Append(std::string &&msg)：LogFile类最重要的接口，让用户向日志文件追加新的消息。其实现逻辑为：在写文件前，先检查当前日志文件大小加上当前消息的长度之和是否会超过创建LogFile对象时指定的日志文件大小上限：如果超过，就将当前文件内容转存到历史文件，并清空当前日志文件（通过Rotate函数），然后，继续把当前消息写入日志文件。 有一点值得说明：获取当前日志文件大小不是通过调用系统函数，而是通过类成员变量cur_size_（构造函数调用一次系统函数为cur_size_赋初值，之后，每次执行Append(), cur_size_都累加消息长度，从而实时追踪日志文件长度）, 这样避免了每次执行Append()时都调用系统函数检查文件长度，从而提高了效率。
void LogFile::Append(std::string&& msg) { double msg_size = (double)msg.size(); if (cur_size_+ msg_size >= max_size_) { Rotate(); } ofs_ << std::forward<std::string>(msg) << std::endl; cur_size_ += msg_size; }
void Rotate()： 转储函数，当前日志文件内容被转存到某个历史日志文件，当前日志文件被清空并被重新打开
void LogFile::Rotate() { if (ofs_.is_open()) { ofs_.close(); } std::string history_file = NextHistoryFile(); std::rename(file_name_.c_str(), history_file.c_str()); ofs_.open(file_name_, std::ofstream::out|std::ofstream::app); cur_size_ = 0; }
std::string NextHistoryFile(): 返回下一个历史日志文件名以用于转存日志文件信息
std::string LogFile::NextHistoryFile() { static int next_file_no = 0; int file_num = (next_file_no++) % max_file_num_; return file_name_ + "." + std::to_string(file_num); }
double LogFile::GetFileSize()： 返回当前日志文件大小(bytes)，当前实现只针对Linux
double LogFile::GetFileSize() { struct stat statbuf; if (stat(file_name_.c_str(), &statbuf) == 0) { return (double)statbuf.st_size; } else { perror("Faild to get log file size"); return 0; } }
针对上述LogFile的实现，我们可以进行如下测试：
#include "logfile.h" int main(void) { LogFile lf("testlogfile.log", 1024, 8); for (auto i = 0; i < 200; i++) { lf.Append(std::to_string(i) + ": this is a very very very very very very very very very very very very very very vvery very very very very ery long log"); } }
测试结果日下：
stephenw@stephenw-devbox1:/local/project/logcpp$ ls -lart testlogfile.log* -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.4 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.3 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.2 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.1 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.7 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.6 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.5 -rw-rw-r-- 1 stephenw stephenw 992 6月 27 23:02 testlogfile.log.0 -rw-rw-r-- 1 stephenw stephenw 124 6月 27 23:02 testlogfile.log
stephenw@stephenw-devbox1:/local/project/logcpp$ tail -n5 testlogfile.log.0 testlogfile.log.1 testlogfile.log.2
==> testlogfile.log.0 <==
194: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
195: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
196: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
197: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
198: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
==> testlogfile.log.1 <==
138: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
139: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
140: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
141: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
142: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
==> testlogfile.log.2 <==
146: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
147: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
148: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
149: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
150: this is a very very very very very very very very very very very very very very vvery very very very very ery long log
标签：targe 成员变量 return 信息 生成 assert https 时间 +=
原文地址：https://www.cnblogs.com/wangwenzhi2019/p/11100331.html
