[Log4cplus-devel] compatibility question concerning log4cplus::tstring

[John L. <jl...@bl...>]

Hello,   I'd like to ask about compatibility of  log4cplus::tstring between 1.0.x and 1.1.x

An application (bind10) has some code like so:

// Convert logging level to string.  If the level is a valid debug level,
// return the string DEBUG, else return the empty string.
log4cplus::tstring
LoggerLevelImpl::logLevelToString(log4cplus::LogLevel level) {
    Level bindlevel = convertToBindLevel(level);
    Severity& severity = bindlevel.severity;
    int& dbglevel = bindlevel.dbglevel;

    if ((severity == DEBUG) &&
        ((dbglevel >= MIN_DEBUG_LEVEL) && (dbglevel <= MAX_DEBUG_LEVEL))) {
        return (tstring("DEBUG"));
    }

    // Unknown, so return empty string for log4cplus to try other conversion
    // functions.
    return (tstring());
}

// Initialization.  Register the conversion functions with the LogLevelManager.
void
LoggerLevelImpl::init() {

    // Get the singleton log-level manager.
    LogLevelManager& manager = getLogLevelManager();

    // Register the conversion functions
    manager.pushFromStringMethod(LoggerLevelImpl::logLevelFromString);
    manager.pushToStringMethod(LoggerLevelImpl::logLevelToString);
}

which compiles correctly against 1.0.x

But compiling against 1.1.x results in 

logger_level_impl.cc:189:1: error: prototype for
         ‘const tstring& isc::log::LoggerLevelImpl::logLevelToString(log4cplus::LogLevel)’
      does not match any in class ‘isc::log::LoggerLevelImpl’
../../../src/lib/log/logger_level_impl.h:115:31: error:
        candidate is: static log4cplus::tstring isc::log::LoggerLevelImpl::logLevelToString(log4cplus::LogLevel)
            In static member function ‘static void isc::log::LoggerLevelImpl::init()’:

Changing the application code to read as follows fixes the problem ...

// Convert logging level to string.  If the level is a valid debug level,
// return the string DEBUG, else return the empty string.
log4cplus::tstring const &
LoggerLevelImpl::logLevelToString(log4cplus::LogLevel level) {

    static const tstring debug_string("DEBUG");
    static const tstring empty_string;

    Level bindlevel = convertToBindLevel(level);
    Severity& severity = bindlevel.severity;
    int& dbglevel = bindlevel.dbglevel;

    if ((severity == DEBUG) &&
        ((dbglevel >= MIN_DEBUG_LEVEL) && (dbglevel <= MAX_DEBUG_LEVEL))) {
        return (debug_string);
    }

    // Unknown, so return empty string for log4cplus to try other conversion
    // functions.
    return (empty_string);
}

but creates two new problems:
  .    code is less general  -   every possible string value which might be returned must be explicitly declared
          (fortunately there are only two  - "DEBUG" and "")
  .  code no longer compiles against 1.0.x  -
logger_level_impl.cc: In static member function 'static void
isc::log::LoggerLevelImpl::init()':
logger_level_impl.cc:217: error: invalid conversion from 'const
log4cplus::tstring& (*)(log4cplus::LogLevel)' to 'log4cplus::tstring
(*)(log4cplus::LogLevel)'
logger_level_impl.cc:217: error:   initializing argument 1 of 'void
log4cplus::LogLevelManager::pushToStringMethod(log4cplus::tstring
(*)(log4cplus::LogLevel))'

Has anyone else run into this?
And is it possible to write the application code for registering and running the logLevelToString() method in such a way that it 
compiles correctly against both log4cplus releases?

John Lumby