logging data

In my processing function, depending upon the activity code , we do some processing  for different activities .  We need to implement logging now. Depending upon the activity code, the data that needs to log would vary.
for ex activity code 01 , log field 1 and field 2
for activity code 02, log field 2 and field 5.

I need some ideas to implement this logging mechanism.

Is it best to have a base logging class and then derive classes out of it for each and every activity code . the derived classes would have data members specific to what it needs to log and a overridenn method persistlog in all the classes would write all of its data members to the disk.

is there any design pattern examples / code that accomplishes some thing like this ?


Thanks for ur help
ramnarsAsked:
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mahesh1402Connect With a Mentor Commented:
you may look into 'Design' of event logger classes which are similar

http://www.codeproject.com/debug/alx_log.asp <== Advanced Logging for all kind of applications
http://www.codeproject.com/system/xeventlog.asp
http://www.codeproject.com/cpp/logdriver.asp

-MAHESH
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rajeev_devinCommented:
>> is there any design pattern examples / code that accomplishes some thing like this ?
Most of the logger code I have gone so far is singleton class. That is, they will have only one object.
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rajeev_devinConnect With a Mentor Commented:
Here is a sample logging mechanism

#include <stdio.h>

#define LOGGER Logger::getInstance()

enum LOGLEVELS{
      LEVEL_01,
      LEVEL_02,
};

class Logger {

public:
      static Logger& getInstance() {

            if (m_pLogger == NULL)
            {
                  m_pLogger = new Logger;
            }
            return *m_pLogger;
      }

      void operator<<(const char* string) const {
            fprintf(m_pLogFile, "%s\n", string);
      }

      const Logger& log(LOGLEVELS level) {
            fprintf(m_pLogFile, "Level : %2d ", level);
            return *this;
      }

      void initialize(FILE* file) {
            m_pLogFile = file;
      }

      void finalize() {
            if (m_pLogFile) {
                  fclose(m_pLogFile);
                  m_pLogFile = NULL;
            }
      }

private:
      Logger() : m_pLogFile(NULL) {
      }

      ~Logger() {

            if (m_pLogFile) {
                  fclose(m_pLogFile);
                  m_pLogFile = NULL;
            }
      }

      static Logger* m_pLogger;
      FILE* m_pLogFile;
};

Logger* Logger::m_pLogger = NULL;

void main()
{
      LOGGER.initialize(stdout); // You can pass your own file object here.
      LOGGER.log(LEVEL_01) << "This is the first log message";
      LOGGER.log(LEVEL_02) << "This is the second log message";
      LOGGER.finalize();
}
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rajeev_devinCommented:
You need to modify the code to match your requirement.
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ramnarsAuthor Commented:
ok. the thing is depending upon the activity code ( there could be  more than 5) , the data that i need to log differs. shoudl i handle that scenario by testing for the activity codes ? I want it to be flexible enough to be modified in the future , in terms of logging data for a new activity code and also in terms of introducing new fields to the data that is being logged.

should i handle all the if conditions in the code where i invoke the logger ? i guess not.

so thats why i was leaning for the idea for invidiual classes for the activity codes and let them decide which fields they want to log


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rajeev_devinCommented:
>> should i handle all the if conditions in the code where i invoke the logger ? i guess not.
As I told you need to extend the logger as per your requirement.

>> so thats why i was leaning for the idea for invidiual classes for the activity codes and let them decide which fields >> they want to log
If you extend the base class into number of derived classes. Your derived classes won't have much work to do.
So, what's the use of extending them.
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rajeev_devinCommented:
The code I posted is not the complete solution for you. You need to extend it.
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AxterConnect With a Mentor Commented:
Check out the following link:
http://axter.com/ezlogger

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