Question

I wrote my own simple class for logging. I understand that I better to use some kind of library (boost.log, log4cpp?) but let’s anyway discuss my simple class:

#include "stdafx.h"
#include "Logger.h"


Logger::Logger(std::string fileName)
{
    logFile.open(fileName);
}


Logger::~Logger(void)
{
    logFile.close();
}


void Logger::Error(std::string message) {
    logFile << message << std::endl;
}

void Logger::Debug(std::string message) {
    logFile << message << std::endl;
}

1. I want my methods to accept variable number of arguments, so I can pass parameters like that "Error code: %x", code. How to do that?
2. I want Debug method to be excluded if LOG_DEBUG compilation symbol is not set. in C# I can just add [Conditional("LOG_DEBUG")] before the method declaration, but now to do that in c++?

upd Regarding 1 i’ve tried that and it works:

void Logger::Debug(std::string message, ...) {
va_list arglist;
fprintf(pFile, message.c_str(), arglist);

Answer 1

I want my methods to accept variable number of arguments, so I can pass parameters like that “Error code: %x”, code. How to do that?

You have two solutions for this:

1. use printf-like formatting. This would require the usage of va_list, va_arg and va_end macros.

2. use operator overloading (as in @Joachim’s answer).

I want Debug method to be excluded if LOG_DEBUG compilation symbol is not set. in C# I can just add [Conditional(“LOG_DEBUG”)] before the method declaration, but now to do that in c++?

You define a logging macro, in two different ways, depending on DEBUG macro definition (or NDEBUG or something similar):

#ifdef DEBUG
#define LOGE(X) Logger::Error(X)
#define LOGD(X) Logger::Debug(X)
#else
#define LOGE(X) 
#define LOGD(X) 
#endif