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 << '
';
}
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());
}