使用Line Pos Info 和 Modern C++ 改进打印日志记录

使用Line Pos Info 和 Modern C++ 改进打印日志记录

使用跟踪值：不管自己是多么的精通，可能仍然使用调试的主要方法之一 printf , TRaCE, outputDebugString, 等…然后扫描输出， 同时调试。

添加有关行号和日志消息来源的文件的信息是一种非常有效的方法，可以为你节省大量时间，在这篇文章将描述一个在visual Studio中特别有用的技巧，在其他IDE/编译器中有所帮助。

还将展示现在C++和C++20如何使代码更好。

常规

在调试C++代码时，将值输出到控制台或输出到窗口并扫描日志非常方便。

 std::cout << "myval: " << val << endl; 

可以通过添加LINE和FILE信息轻松增强此技术，这样就可以看到那条消息的来源。扫描大量日志时，这可能非常方便。

为什么会这么重要呢？就每个人来说，当我们试图查找某些日志输出的来源时，我们已经失去了很多时间。当我们看到一条消息时，我们会复制他，搜索解决方案，然后通常在滚动后终于找到了正确的代码行。那么有没有更为简便的方法呢？

将使用“标准”C++实现此代码，然后转到现代C++，最后看看C++20将会发生什么？

log4cpp 中添加需要打印的行号，文件名，函数名 (标准C++)

使用log4cpp中的Category的debug, error, info , warn 等方法输出，需要调试的信息：

root.debug(“Message”);

但最后用宏包装上面的函数：

#define logWarn(msg)\ my_logWarn(__LINE__,__FILE__,__FUNCTION__,msg)

通过logWarn(msg)使用；

上面代码调用logWarn(msg)内部调用的函数my_llogWarn。

为什么定义一个宏？当然，方便。否则，必须手动传递行号和文件名。无法在内部获取文件和行，my_logWarn 因为它始终指向实现的源代码my_logWarn而不是调用它的代码。

什么是 __ FILE __ 和 __ LINE __ ? 在vistual Studio 中，这下可以在代码中使用的预定义宏。顾名思义，他们会扩展到源代码的文件名和给定翻译单元中的确定行。要控制 __ FILE __ 宏， 可以使用编译器选项 /FC 。该选项使文件名更长（完整路径）或更短（相对于解决方案目录），请注意,/FC使用“编译并继续“时暗示。

注意， __ FILE __ 并且 __ LINE __ 也由标准制定，因此其他编译器也应该实现它。

 void my_logWarn(int line,const char *filename,const char *funcName, const char *msg)
 {
      Mylog *log = Mylog::getInstance();

      string tempMsg = msg;
      tempMsg = tempMsg + " doucument name:" + std::string(filename) + " this is line: " + std::to_string(line) + " func name: " + string(funcName);

      log->Warn(tempMsg.c_str());
 }

C++ 20

在C++20中有std::source_location

新的库类型声明如下：

 struct source_location{
     static constexpr source_location current () noexcept;
     constexpr uint_lest32_t line() const noexcept;
     constexpr uint_lest32_t column() const noexcept;
     constexpr const char * filename() const noexcept;
     constexpr const char *function_name() const noexcept;
 }

一个基本的使用例子：

 #include <iostream>
 #include <string_view>
 #include <experimental/source_location>
 ​
 using namespace std;
 using namespace std::experimental;
 ​
 void log(const string_view& message,
       const source_location& location = source_location::current())
 {
     std::cout << "info:"
               << location.file_name() << ":"
               << location.line() << " "
               << location.function_name() << " "
               << message << '\n';
 }
 ​
 int main()
 {
     log("Hello world!");
 ​
     // another log
     log("super extra!");
 }

　　

总结

简单介绍了增强的printf样式和日志记录

起初，使用的主要是C风格的标准代码，后来使用了现代C++进行更新，最后了使用了C++20中的source_location引入的新类型实现。

随着soure_location使我们可以跳过使用__ FILE __ 和 __ LINE __ 预定义宏,不过，日志宏（#define Log(…)) 是有帮助的，因为他可以隐藏于位置信息缺省参数。

base C++:

#pragma once

#define logInfo(msg)\
    my_logInfo(__LINE__,__FILE__,__FUNCTION__,msg)
#define logWarn(msg)\
    my_logWarn(__LINE__,__FILE__,__FUNCTION__,msg)
#define logError(msg)\
    my_logError(__LINE__,__FILE__,__FUNCTION__,msg)
#define logDebug(msg)\
    my_logDebug(__LINE__,__FILE__,__FUNCTION__,msg)
#include <stdlib.h>
#include <iostream>
#include <string>
using std::cout;
using std::endl;
using std::string;

#include <log4cpp/Category.hh>
#include <log4cpp/Priority.hh>
#include <log4cpp/FileAppender.hh>
#include <log4cpp/RollingFileAppender.hh>
#include <log4cpp/OstreamAppender.hh>
#include <log4cpp/PatternLayout.hh>

using namespace log4cpp;
class Mylog
{
public:
    void Warn(const char *msg);
    void Error(const char *msg);
    void Debug(const char * msg);
    void Info(const char * msg);

    static Mylog * getInstance()
    {
        if(_pInstance == nullptr){
            _pInstance = new Mylog();
        }
        return _pInstance;
    }
    static void destory()
    {

        if(_pInstance)
        {

            Category::shutdown();
        }
    }
private:
    Mylog():root(Category::getRoot()){
        PatternLayout * ptnLayout1 = new PatternLayout();
        ptnLayout1->setConversionPattern("%d [%p] %m%n");
        PatternLayout * ptnLayout2 = new PatternLayout();
        ptnLayout2->setConversionPattern("%d [%p] %m%n");
        PatternLayout * ptnLayout3 = new PatternLayout();
        ptnLayout3->setConversionPattern("%d [%p] %m%n");

        OstreamAppender * ostreamAppender = new OstreamAppender("ostreamAppender",&cout);
        ostreamAppender->setLayout(ptnLayout1);

        FileAppender *fileAppender = new FileAppender("fileAppender","davarain.log");
        fileAppender->setLayout(ptnLayout2);

        RollingFileAppender * rollingAppender = new RollingFileAppender("rollingAppender","rollingAppender.log",5*1024,2);
        rollingAppender->setLayout(ptnLayout3);

        root.setAppender(ostreamAppender);
        root.addAppender(fileAppender);
        root.addAppender(rollingAppender);

        root.setPriority(Priority::DEBUG);
        cout << "Mylog()" << endl;
    }
    ~Mylog()
    {
        cout << "~Mylog()" << endl;
    }
private:
    Category & root;
    static Mylog * _pInstance;
};

Mylog * Mylog::_pInstance = nullptr;

void Mylog::Info(const char *msg)
{
    root.info(msg);
}
void Mylog::Warn(const char *msg)
{
    root.warn(msg);
}
void Mylog::Debug(const char *msg)
{
    root.debug(msg);
}
void Mylog::Error(const char *msg)
{
    root.error(msg);
}
void my_logInfo(int line, const char *filename, const char *funcName, const char *msg)
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + std::string(filename) + " this is line: " + std::to_string(line) + " func name: " + string(funcName);
    log->Info(tempMsg.c_str());
}
void my_logError(int line,const char *filename,const char *funcName, const char *msg)
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + std::string(filename) + " this is line: " + std::to_string(line) + " func name: " + string(funcName);
    log->Error(tempMsg.c_str());
}
void my_logWarn(int line,const char *filename,const char *funcName, const char *msg)
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + std::string(filename) \
              + " this is line: " + std::to_string(line) + " func name: " + string(funcName);
    log->Warn(tempMsg.c_str());
void my_logDebug(int line, const char *filename, const char *funcName,const char *msg)
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + std::string(filename) + " this is line: " + std::to_string(line) + " func name: " + string(funcName);
    log->Debug(tempMsg.c_str());
}

　　C++20:

#pragma once
/*
#define logInfo(msg) \
    my_logInfo(__LINE__,__FILE__,__FUNCTION__,msg)
#define logWarn(msg)\
    my_logWarn(__LINE__,__FILE__,__FUNCTION__,msg)
#define logError(msg)\
    my_logError(__LINE__,__FILE__,__FUNCTION__,msg)
#define logDebug(msg)\
    my_logDebug(__LINE__,__FILE__,__FUNCTION__,msg)
*/
#include <stdlib.h>
#include <iostream>
#include <string>
#include <experimental/source_location>
using std::cout;
using std::endl;
using std::string;
using namespace std::experimental;

#include <log4cpp/Category.hh>
#include <log4cpp/Priority.hh>
#include <log4cpp/FileAppender.hh>
#include <log4cpp/RollingFileAppender.hh>
#include <log4cpp/OstreamAppender.hh>
#include <log4cpp/PatternLayout.hh>

using namespace log4cpp;
class Mylog
{
public:
    void Warn(const char *msg);
    void Error(const char *msg);
    void Debug(const char * msg);
    void Info(const char * msg);

    static Mylog * getInstance()
    {
        if(_pInstance == nullptr){
            _pInstance = new Mylog();
        }
        return _pInstance;
    }
    static void destory()
    {

        if(_pInstance)
        {

            Category::shutdown();
        }
    }
private:
    Mylog():root(Category::getRoot()){
        PatternLayout * ptnLayout1 = new PatternLayout();
        ptnLayout1->setConversionPattern("%d [%p] %m%n");
        PatternLayout * ptnLayout2 = new PatternLayout();
        ptnLayout2->setConversionPattern("%d [%p] %m%n");
        PatternLayout * ptnLayout3 = new PatternLayout();
        ptnLayout3->setConversionPattern("%d [%p] %m%n");

        OstreamAppender * ostreamAppender = new OstreamAppender("ostreamAppender",&cout);
        ostreamAppender->setLayout(ptnLayout1);

        FileAppender *fileAppender = new FileAppender("fileAppender","davarain.log");
        fileAppender->setLayout(ptnLayout2);

        RollingFileAppender * rollingAppender = new RollingFileAppender("rollingAppender","rollingAppender.log",5*1024,2);
        rollingAppender->setLayout(ptnLayout3);

        root.setAppender(ostreamAppender);
        root.addAppender(fileAppender);
        root.addAppender(rollingAppender);

        root.setPriority(Priority::DEBUG);
        cout << "Mylog()" << endl;
    }
    ~Mylog()
    {
        cout << "~Mylog()" << endl;
    }
private:
    Category & root;
    static Mylog * _pInstance;
};

Mylog * Mylog::_pInstance = nullptr;

void Mylog::Info(const char *msg)
{
    root.info(msg);
}
void Mylog::Warn(const char *msg)
{
    root.warn(msg);
}
void Mylog::Debug(const char *msg)
{
    root.debug(msg);
}
void Mylog::Error(const char *msg)
{
    root.error(msg);
}
void logInfo(const char *msg,const source_location& location= source_location::current())
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + location.file_name() + " this is line: " + std::to_string(location.line()) + " func name: " + location.function_name();
    log->Info(tempMsg.c_str());
}
void logError(const char *msg, const source_location& location = source_location::current())
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + location.file_name() + " this is line: " + std::to_string(location.line()) + " func name: " + location.function_name();
    log->Error(tempMsg.c_str());
}
void logWarn(const char *msg,const source_location& location = source_location::current())
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + location.file_name() + " this is line: " + std::to_string(location.line()) + " func name: " + location.function_name();
    log->Warn(tempMsg.c_str());
}
void logDebug(const char *msg,const source_location& location = source_location::current())
{
    Mylog *log = Mylog::getInstance();
    string tempMsg = msg;
    tempMsg = tempMsg + " doucument name:" + location.file_name() + " this is line: " + std::to_string(location.line()) + " func name: " + location.function_name();
    log->Debug(tempMsg.c_str());
}