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

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

Hello Václav and thanks for the patch.

We've tried it and does indeed fix the problems we found and we can now build our same source tree against log4cplus 1.0.x and against the latest log4cplus 1.1.7+patch.   Many thanks.

John Lumby
Database Architect
BlueCat Networks Inc.

________________________________________
From: Václav Zeman [vha...@gm...]
Sent: Thursday, August 02, 2012 6:03 AM
To: John Lumby
Cc: log...@li...
Subject: Re: [Log4cplus-devel] compatibility question concerning log4cplus::tstring

On 2 August 2012 11:00, Václav Zeman wrote:
> On 1 August 2012 17:13, John Lumby wrote:
>> Hello,   I'd like to ask about compatibility of  log4cplus::tstring between 1.0.x and 1.1.x
> As I have written in reply in another thread, my intention has always
> been to keep log4cplus source compatible between versions.
>
>>
>> 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 "")
> I do not regard this as a problem. The set of log levels is intended
> to be small. The change of return type to reference to tstring is
> there for speed.
>
>>   .  code no longer compiles against 1.0.x  -
> This is a problem.  What you have discovered breaks the source
> compatibility intention and I am going to fix it by allowing both old
> and new callbacks.
>
>> 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?
I am attaching a patch that should allow using callbacks with both return types.

If there is any other source incompatibility, please let me know.

--
VZ