Log4cpp record log repeatly

Question

I am using log4cpp to create a Log class, which is designed in the singleton mode. Here is my Log.h

#include <cstdio>
#include <cstring>
#include <cstdarg>
#include <log4cpp/Category.hh>
#include <log4cpp/Appender.hh>
#include <log4cpp/FileAppender.hh>
#include <log4cpp/Priority.hh>
#include <log4cpp/PatternLayout.hh>

class CtagentLog
{
public:
    static CtagentLog& getInstance() {
        static CtagentLog instance;
        return instance;
    }

    void Log(int type, char *content);

private:
    CtagentLog();
    CtagentLog(CtagentLog const&);
    CtagentLog& operator=(CtagentLog const &);
    ~CtagentLog();


//  char *log_file;
//  log4cpp::PatternLayout *plt;
//  log4cpp::Appender *app;
        void itoa(int n, char* str, int radix);

};

and this is my Log.cpp file:

#include "Log.h"


CtagentLog::CtagentLog()
{
}

CtagentLog::~CtagentLog()
{

}

/*
 * type=1 ERROR
 * type=2 WARN
 * type=3 INFO
 */
void CtagentLog::Log(int type, char *content)
{
    log4cpp::PatternLayout *plt = new log4cpp::PatternLayout();
    plt->setConversionPattern("[%d] %p %c %x: %m%n");
    log4cpp::Appender *app = new log4cpp::FileAppender("fileAppender", "test.log");
    app->setLayout(plt);

    log4cpp::Category &root = log4cpp::Category::getRoot().getInstance("Test");
    root.addAppender(app);
    root.setPriority(log4cpp::Priority::DEBUG);
    switch(type){
        case 1: root.error(content); break;
        case 2: root.warn(content); break;
        case 3: root.info(content); break;
        default: root.info(content); break;
    }
}

And finally my testmain.cpp:

#include "Log.h"
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>


void *func1(void *arg)
{
    printf("thread 1\n");
}

void *func2(void *arg)
{
    printf("thread 2\n");
}

int main(void)
{
    pthread_t tid1;
    pthread_t tid2;

    pthread_create(&tid1, NULL, func1, NULL);
    pthread_join(tid1, NULL);
    CtagentLog::getInstance().Log(1,"Create Thread 1 Return");
    pthread_create(&tid2, NULL, func2, NULL);
    pthread_join(tid2, NULL);
    CtagentLog::getInstance().Log(1,"Create Thread 2 Return");

    return 0;

}

Compile with g++ -g Main.cpp Log.cpp -lpthread -llog4cpp, and run it. the output is :

# ./a.out 
thread 1
thread 2

but the test.log is like this:

[2013-07-29 21:32:34,101] ERROR Test : Create Thread 1 Return
[2013-07-29 21:32:34,101] ERROR Test : Create Thread 2 Return
[2013-07-29 21:32:34,101] ERROR Test : Create Thread 2 Return

I want to know why the second call log twice. Am I using the log4cpp wrong?

Answer 1

It's because you add new appenders every time in the Log function. Each new appender, well, append the output. If you called it a third time you would have gotten three outputs.

Things like adding appenders, setting layouts or other such one-time configuration should be done only once, preferably in a constructor or initialization function.