How to enable/disable spdlog logging in code?

Question

I am creating c++ library modules in my application. To do logging, I use spdlog. But in a production environment, I don't want my lib modules to do any logging. One way to achieve turning on/off would be to litter my code with #ifdef conditionals like...

#ifdef logging
  // call the logger here.
#endif

I am looking for a way to avoid writing these conditionals. May be a wrapper function that does the #ifdef checking and write it. But the problem with this approach is that I have to write wrappers for every logging method (such as info, trace, warn, error, ...)

Is there a better way?

Answer 1

You can disable logging with set_level():

auto my_logger = spdlog::basic_logger_mt("basic_logger", "logs/basic.txt");

#if defined(PRODUCTION)
    my_logger->set_level(spdlog::level::off);
#else
    my_logger->set_level(spdlog::level::trace);
#endif

spdlog::register_logger(my_logger);

Answer 2

You can disable all logging before you compile the code by adding the following macro (before including spdlog.h):

#define SPDLOG_ACTIVE_LEVEL SPDLOG_LEVEL_OFF
#include<spdlog.h>

It is explained as a comment in the file https://github.com/gabime/spdlog/blob/v1.x/include/spdlog/spdlog.h :

//
// enable/disable log calls at compile time according to global level.
//
// define SPDLOG_ACTIVE_LEVEL to one of those (before including spdlog.h):
// SPDLOG_LEVEL_TRACE,
// SPDLOG_LEVEL_DEBUG,
// SPDLOG_LEVEL_INFO,
// SPDLOG_LEVEL_WARN,
// SPDLOG_LEVEL_ERROR,
// SPDLOG_LEVEL_CRITICAL,
// SPDLOG_LEVEL_OFF
//

Using this macro will also speed up your productive code because the logging calls are completely erased from your code. Therefore this approach may be better than using my_logger->set_level(spdlog::level::off);

However, in order for the complete code removal to work you need to use either of the macros when logging:

SPDLOG_LOGGER_###(logger, ...)

SPDLOG_###(...)

where ### is one of TRACE, DEBUG, INFO, WARN, ERROR, CRITICAL.

The latter macro uses the default logger spdlog::default_logger_raw(), the former can be used with your custom loggers. The variadic arguments ... stand for the regular arguments to your logging invocation: the fmt string, followed by some values to splice into the message.

Answer 3

I don't know spdlog.

However, you may define a macro in one of your common used include file, to replace the logcall by nothing, or a call to an empty inline function which the compiler optimizer will eliminate.

in "app.h"

#ifndef LOG

#ifdef logging
#define LOG spdlog
#endif

#ifndef logging
#define LOG noop
#endif

#endif

Did you get the idea?

This let most of your code untouched