format-string.cpp

This example shows logging using the {fmt} library.

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#include <stdlib.h>
#include <log4cxx/logger.h>
#include <log4cxx/basicconfigurator.h>
#include <locale.h>
#if LOG4CXX_USING_STD_FORMAT
#include <format>
#else
#include <fmt/core.h>
#include <fmt/color.h>
#include <fmt/ostream.h>
#endif
#include <iomanip>
 
struct MyStruct {
        int x;
};
 
std::ostream& operator<<( std::ostream& stream, const MyStruct& mystruct ){
        stream << "[MyStruct x:" << mystruct.x << "]";
        return stream;
}
 
#if LOG4CXX_USING_STD_FORMAT
template <typename Char>
struct basic_ostream_formatter
    : std::formatter<std::basic_string_view<Char>, Char>
{
    template <typename T, typename OutputIt>
    auto format(const T& value, std::basic_format_context<OutputIt, Char>& ctx) const -> OutputIt
    {
        std::basic_stringstream<Char> ss;
        ss << value;
        return std::formatter<std::basic_string_view<Char>, Char>::format(ss.view(), ctx);
    }
};
template <> struct std::formatter<MyStruct> : basic_ostream_formatter<char> {};
#elif FMT_VERSION >= (9 * 10000)
template <> struct fmt::formatter<MyStruct> : ostream_formatter {};
#endif
 
int main()
{
    setlocale(LC_ALL, "");
 
    using namespace log4cxx;
    BasicConfigurator::configure();
    auto rootLogger = Logger::getRootLogger();
 
    LOG4CXX_INFO_FMT( rootLogger, "This is a {} mesage", "test" );
#if !LOG4CXX_USING_STD_FORMAT
    LOG4CXX_INFO_FMT( rootLogger, fmt::fg(fmt::color::red), "Messages can be colored" );
#endif
    LOG4CXX_INFO_FMT( rootLogger, "We can also align text to the {:<10} or {:>10}", "left", "right" );
 
    MyStruct mine{ 42 };
    LOG4CXX_INFO_FMT( rootLogger, "This custom type {} can also be logged, since it implements operator<<", mine );
 
    LOG4CXX_INFO( rootLogger, "Numbers can be formatted with excessive operator<<: "
                  << std::setprecision(3) << 22.456
                  << " And as hex: "
                  << std::setbase( 16 ) << 123 );
    LOG4CXX_INFO_FMT( rootLogger, "Numbers can be formatted with a format string {:.1f} and as hex: {:x}", 22.456, 123 );
 
    return 0;
}