Minimalistic C++11 logger with per-user-class configuration

miculog.config

/**
 * This file is intended for miculog per-class configuration
 */

/* remove this message from your own copy of miculog.config 				*/
#pragma message "Default miculog configuration is in use"


/* add forward declaration of your classes here, 
 * embrace classes in namespaces, as needed 								
 * 
 * 									to enable code	remove space  there ->	* /
class myclass;

namespace miculog {
template<> struct class_log_levels<myclass> {
	static constexpr auto value = levels<
		level::warn, level::error, level::fail>::value;
};
template<> struct appender<myclass> {
	static void log(const char* fmt, ...) noexcept;
};
}

// as an lazy option you may use macro SET_MIN_LOGLEVEL

/// Sets min log level for a given class CLASS. 
/// CLASS must be declared prior to use of this macro
#define SET_MIN_LOGLEVEL(CLASS, LEVEL) 										\
namespace miculog {															\
template<> struct class_log_levels<CLASS> {									\
	static constexpr auto value = from<LEVEL>::value;						\
};}																			\

class myclass2;
SET_MIN_LOGLEVEL(myclass2, level::warn) 
// */

miculog.cpp

/*
 * Copyright (C) 2017 Eugene Hutorny <eugene@hutorny.in.ua>
 *
 * miculog.hpp - simple logging facilities
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * https://opensource.org/licenses/MIT
 */

#include <cstdio>
#include <cstdarg>

#include "miculog.hpp"

namespace miculog {
inline constexpr unsigned char operator+(level lvl) noexcept {
	return static_cast<unsigned char>(lvl);
}
namespace details {

static const char * const names[1 + +level::none]  = {
	"!TRACE: ",
	"!DEBUG: ",
	"!INFO : ",
	"!WARN : ",
	"!ERROR: ",
	"!FAIL : ",
	"!?NONE: "
};

void default_appender::log(level lvl, const char* fmt, ...) noexcept {
	if( lvl <= level::none )
		fputs(names[+lvl], stdout);
	va_list args;
	va_start(args, fmt);
	vfprintf(stdout, fmt, args);
	va_end(args);
}

}}

miculog.hpp

/*
 * Copyright (C) 2017 Eugene Hutorny <eugene@hutorny.in.ua>
 *
 * miculog.hpp - simple logging facilities
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * https://opensource.org/licenses/MIT
 */

#ifndef MICULOG_HPP_
#define MICULOG_HPP_
/*
 * Simple and configurable logging facilities
 *
 * Concepts
 *	Classes defined here facilitate logging functionality with
 *	compile-time configurable levels and appenders on per-user-class basis.
 *	Logging statement with opted off levels are completely removed from
 *	generated code by the compiler on optimization phase. If logging is
 *	turned off completely, compiler builds application without any appenders
 *	provided
 *
 * Usage
 *  Define a static instance of Log class in the compilation unit where it will
 *  be used:
 *
 *  	static miculog::Log<myclass> log;
 *
 *	Use methods, available in log:
 *
 *		log.error("error code:%d\n", err);
 *
 *  This will emit log statements ending up in default appender, which
 *  calls vprintf for levels error and fail
 *
 *  To change enabled levels, specialize template class_log_levels
 *  as the following:
 *
 *  	namespace miculog {
 *		template<> struct class_log_levels<myclass> {
 *			static constexpr auto value = levels<level::info>::value;
 *		};}
 *
 *	To change appender specialize template appender as the following:
 *
 *  	namespace miculog {
 *		template<> struct appender<myclass> {
 *	    	static void log(const char* fmt, ...) noexcept;
 *	    };}
 *
 *	and implement appender<myclass>::log
 *
 *	Generally, you may add these template specializations in any place in
 *	your code before the actual instantiation of template Log,
 *	Recommended practice is to include them in your own copy of
 *	micolug.config file, which should be found in the include path
 *	before the one provided with this library
 *
 *	You may also replace default appender with a suitable implementation
 *  simply by removing miculog.cpp from the build and providing your own
 *  implementation elsewhere
 */

namespace miculog {

enum class level : unsigned char {
	trace,
	debug,
	info,
	warn,
	error,
	fail,
	none
};

namespace details {

/* all log calls end up in this function, implemented by the user	*/

struct default_appender {
	static void log(level, const char* fmt, ...) noexcept
										__attribute__ ((format (printf, 2, 3)));
};

template<typename V, typename T, T...>
struct enumset;

template<typename V, typename T>
struct enumset<V, T> {
	static constexpr const V value = 0;
};

template<typename V, typename T>
static constexpr const V shift(int v, T t) noexcept {
	return static_cast<V>(v) << static_cast<V>(t);
}

template<typename V, typename T, T t>
struct enumset<V, T, t> {
	static constexpr const V value = { shift<V>(1, t) };
};

template<typename V, typename T, T t, T ... l>
struct enumset<V, T, t, l...> {
	static constexpr const V value = {
		(shift<V>(1, t)) | enumset<V, T, l...>::value };
};

template<typename V>
static inline bool constexpr is_set(V v, level t) noexcept {
	return v & (static_cast<V>(1) << static_cast<V>(t));
}
}

template<class C> struct appender: public details::default_appender {};

template<level t>
struct from {
	static constexpr const unsigned char value = {
		t == level::none ? 0 : details::shift<unsigned char>(-1, t) };
};

template<level ... list>
struct levels: details::enumset<unsigned char, level, list...> {};

//TODO switch to variable template when compilers catch up on C++14
template<class C> struct class_log_levels {
	static constexpr auto value = from<level::error>::value;
};

template<class C>
struct Log {
	typedef appender<C> appender;

	static inline constexpr const auto enabled(level lvl) {
		return details::is_set(levels, lvl);
	}
	template<typename ... T>
	inline static void trace(const char* fmt, T ... args) noexcept {
		if( enabled(level::trace) )
			appender::log(level::trace, fmt, args...);
	}
	template<typename ... T>
	inline static void debug(const char* fmt, T ... args) noexcept {
		if( enabled(level::debug) )
			appender::log(level::debug, fmt, args...);
	}
	template<typename ... T>
	inline static void info(const char* fmt, T ... args) noexcept {
		if( enabled(level::info) )
			appender::log(level::info, fmt, args...);
	}
	template<typename ... T>
	inline static void warn(const char* fmt, T ... args) noexcept {
		if( enabled(level::warn) )
			appender::log(level::warn, fmt, args...);
	}
	template<typename ... T>
	inline static void error(const char* fmt, T ... args) noexcept {
		if( enabled(level::error) )
			appender::log(level::error, fmt, args...);
	}
	template<typename ... T>
	inline static void fail(const char* fmt, T ... args) noexcept {
		if( enabled(level::fail) )
			appender::log(level::fail, fmt, args...);
	}
	template<typename Bool, typename ... T>
	inline static void warn_if(Bool cond, const char* fmt, T ... args)
			noexcept {
		if( enabled(level::warn) )
			if (cond)
				appender::log(level::warn, fmt, args...);
	}
	template<typename Bool, typename ... T>
	inline static void error_if(Bool cond, const char* fmt, T ... args)
			noexcept {
		if( enabled(level::error) )
			if( cond )
				appender::log(fmt, args...);
	}
	template<typename Bool, typename ... T>
	inline static void fail_if(Bool cond, const char* fmt, T ... args)
			noexcept {
		if( enabled(level::fail) )
			if( cond )
				appender::log(level::fail, fmt, args...);
	}
private:
	static constexpr unsigned char levels = class_log_levels<C>::value;
};
}
#include <miculog.config>
#endif /* MICULOG_HPP_ */