Logging & Filters … etc

I think that is extremely beneficial for every desktop application having an flexible yet powerful logging system.

This can “log” to a file, to a console (internal or not) or both. Anyway, the most important thing are the different log levels, and filters.

Let’s say that we have Text, Info, Warning, Error … each represents an level. Then we can setup a filter to “show” only the Warnings, or the Errors supressing all the other messages. This is extremly useful if you have bunch messages showing up in your log file / console.

Now let’s see some code

#define SAFE_ARRAY_DELETE(x) if(x) {delete [] x; x=NULL;}

#define INRANGE(x,min,max) ( (x >= min) && (x < max) )

namespace Log
{
    const int Text        = 0;
    const int Info         = 1;
    const int Warning   = 2;
    const int Error       = 3;
       
    // used only by the filtering
    const int Any        = 4;

};

static int g_logFilter = Log::Any;

void setConsoleLogFilter( const int logFilter )
{
    if( INRANGE(logFilter,0,5) )
    {
        g_logFilter = logFilter;
        return;
    }
    g_logFilter = Log::Any;
}
 
void consoleLog( const int logLevel, const char *msg, ... )
{
    va_list ap;

    // is filtering turned on?
    if( g_logFilter != Log::Any && g_logFilter != logLevel )
    {
        return;
    }

    char *text = new char[ 2048 ];
    assert( text );
 
    memset(text,0,sizeof(text));
 
    va_start(ap, msg);
        vsprintf(text, msg, ap);
    va_end(ap);
 
    switch( logLevel )
    {
        case Log::Info:
            printf( "INFO: %s\n", text );               
            break;

        case Log::Warning:
            printf( "WARNING: %s\n", text );               
            break;
       
        case Log::Error:
            printf( "ERROR: %s\n", text );               
            break;
           
        default:
            printf( "%s\n", text );               
            break;
    }

    SAFE_ARRAY_DELETE( text );
}

This is very very straightforward … it’s C++, but it can be adapted to C, by replacing the memory managment stuff … new with malloc, delete [] with free and moving out the constants into an enum

It works out great for me, and I use something very very similar to this on a day to day basis

Happy coding!