日志文件的作用

日志文件可以很好的帮我们显示出程序运行的信息,例如,进程pid,运行时间,运行状况等,通过日志记录程序的执行路径、变量值、函数调用等，可以帮助我们快速定位和修复代码中的错误。

简单的日志文件编写

下面是用C/C++编写的一段日志文件: Log.hpp

#pragma once 

//日志文件

#include<iostream>
#include<cstdio>
#include<stdarg.h>
#include<ctime>
#include<fstream>
#include <sys/stat.h>
#include <sys/types.h>

enum  //日志等级设置 
{
    
     
    Debug = 0,  //调试等级
    Info,  //常规
    Warning,  
    Error,
    Fatal  //服务器 
};

enum   //设置打印风格
{
    
    
    Screen = 0,  //打印到显示器
    OneFile,    //打印到一个文件里
    ClassFile   //分文件打印
};

const int defauleStyle = Screen;  //默认打印到屏幕上
const std::string defaultFilename = "log.";
const std::string logdir = "log";

std::string LevelToString(int level)
{
    
    
    switch(level)
    {
    
    
        case Debug:
        return "Debug";
        case Info:
        return "Info";
        case Warning:
        return "Warning";
        case Error:
        return "Error";
        case Fatal:
        return "Fatal";
        default:
        return "Unknow";
    }
}

std::string localTime()
{
    
    
    time_t curtime = time(0);
    struct tm *t = localtime(&curtime);
    char time_buffer[128];
    snprintf(time_buffer,sizeof(time_buffer),"%d-%d-%d %d:%d:%d",\
                                            t->tm_year+1900,t->tm_mon+1,t->tm_mday,\
                                            t->tm_hour,t->tm_min,t->tm_sec);
    return time_buffer;
}


class Log
{
    
    
public:
    Log():style(defauleStyle),filename(defaultFilename)
    {
    
    
        mkdir(logdir.c_str(),0775); //创建log目录用以记录日志文件
    }


    //设置打印风格,默认打印到屏幕
    void Enable(int sty)
    {
    
    
        style = sty;
    }

    void WriteOnefile(const std::string& logname, const std::string &message)
    {
    
    
        std::ofstream out(logname,std::ios::app); //创建文件,并以追加的方式打印内容
        if(!out.is_open()) return;
        out.write(message.c_str(),message.size()); //向目标文件中输出内容

        out.close();
    }

    void WriteClassfile(const std::string& level,const std::string &message)
    {
    
    
        std::string logname = logdir;  //写入文件名的时候加上路径,就会直接在所写路径下进行输出
        logname += '/';
        logname += filename;
        logname += level;
        WriteOnefile(logname,message);
    }   

    void Writelog(const std::string &level,const std::string &message)
    {
    
    
        switch (style)
        {
    
    
            case Screen: //默认打印到屏幕
                std::cout<<message<<std::endl;
                break;
            case OneFile:  //默认打印到log.all文件中
                WriteClassfile("all",message);
                break;
            case ClassFile:  //默认打印到各类日志文件中
                WriteClassfile(level,message);
                break;
            default:
                break;
        }
    }

    //使用可变参数
    void LogMessage(int level,const char* format,...)
    {
    
    
        char leftbuffer[1024]; // 这里打印日志等级,时间  到leftguffer
        snprintf(leftbuffer, sizeof(leftbuffer), "[%s] [%s]", LevelToString(level).c_str(), localTime().c_str());
        
        char rightbuffer[1024];  // 这里打印输入参数的内容  到rightbuffer
        va_list args;
        va_start(args,format); //初始化可变参数列表 
        //此时args指向了可变参数部分 , 将参数中的信息输入到字符串mess中
        vsnprintf(rightbuffer,sizeof(rightbuffer),format,args);
        va_end(args);

        //将信息合体
        std::string message(leftbuffer);
        message += rightbuffer;

        //打印内容
        Writelog(LevelToString(level),message);
    }
    ~Log()
    {
    
    }
public:
    int style;//打印风格  上面默认设置为打印到屏幕
    std::string filename;   //文件名默认为: log.

};

调试代码:
test.cc

#include<iostream>
#include"Log.hpp"
#include <unistd.h>

using namespace std;

void testLog()
{
    
    
    Log log;
    log.Enable(ClassFile);
    log.LogMessage(Debug," i am %d \n",getpid());
    log.LogMessage(Info," i am %d \n",getpid());
    log.LogMessage(Warning," i am %d \n",getpid());
    log.LogMessage(Error," i am %d \n",getpid());
    log.LogMessage(Fatal," i am %d \n",getpid());
    log.LogMessage(Debug," i am %d \n",getpid());
    log.LogMessage(Info," i am %d \n",getpid());
    log.LogMessage(Warning," i am %d \n",getpid());
    log.LogMessage(Error," i am %d \n",getpid());
    log.LogMessage(Fatal," i am %d \n",getpid());
    log.LogMessage(Debug," i am %d \n",getpid());
    log.LogMessage(Info," i am %d \n",getpid());
    log.LogMessage(Warning," i am %d \n",getpid());
    log.LogMessage(Error," i am %d \n",getpid());
    log.LogMessage(Fatal," i am %d \n",getpid());
}

int main()
{
    
    
   testLog();

    return 0;
}

测试结果:

可以看到,log目录下有各个日志文件,每个日志文件中有不同的内容
如:log.Debug