C++ source_locationによるモダンなログ出力とエラーハンドリングの実装手法

#include <iostream>
#include <source_location>
#include <string_view>

void log_message(std::string_view message, 
                 const std::source_location location = std::source_location::current()) {
    std::cout << "File: " << location.file_name() << " ("
              << location.line() << ":"
              << location.column() << ") `"
              << location.function_name() << "`: "
              << message << std::endl;
}

int main() {
    log_message("Hello, Source Location!");
    return 0;
}

File: main.cpp (14:16) `main`: Hello, Source Location!

#include <iostream>
#include <format>
#include <source_location>
#include <string_view>
#include <chrono>

enum class LogLevel {
    Info,
    Warning,
    Error
};

class Logger {
public:
    static void log(LogLevel level, std::string_view message, 
                   const std::source_location loc = std::source_location::current()) {
        auto now = std::chrono::system_clock::now();
        std::string level_str = toString(level);
        
        // std::formatを使用して整形
        std::string output = std::format(
            "[{:%Y-%m-%d %H:%M:%S}] [{}] [{}:{}] {}: {}",
            now, level_str, loc.file_name(), loc.line(), loc.function_name(), message
        );
        
        std::cout << output << std::endl;
    }

private:
    static std::string toString(LogLevel level) {
        switch (level) {
            case LogLevel::Info: return "INFO";
            case LogLevel::Warning: return "WARN";
            case LogLevel::Error: return "ERROR";
            default: return "UNKNOWN";
        }
    }
};

void process_data() {
    Logger::log(LogLevel::Info, "データ処理を開始します");
    // 何らかの処理
    Logger::log(LogLevel::Warning, "リソースの消費量が増加しています");
}

int main() {
    process_data();
    return 0;
}

[2026-04-30 10:00:00] [INFO] [main.cpp:40] process_data: データ処理を開始します
[2026-04-30 10:00:01] [WARN] [main.cpp:42] process_data: リソースの消費量が増加しています

#include <stdexcept>
#include <string>
#include <source_location>
#include <iostream>

class DetailedException : public std::runtime_error {
public:
    DetailedException(const std::string& message, 
                      const std::source_location location = std::source_location::current())
        : std::runtime_error(message), location_(location) {}

    const std::source_location& location() const noexcept {
        return location_;
    }

    std::string full_report() const {
        return std::format("Error: {} at {}:{} ({})", 
                           what(), location_.file_name(), location_.line(), location_.function_name());
    }

private:
    std::source_location location_;
};

void risky_operation() {
    throw DetailedException("致命的なエラーが発生しました");
}

int main() {
    try {
        risky_operation();
    } catch (const DetailedException& e) {
        std::cerr << "例外捕捉: " << e.full_report() << std::endl;
    }
    return 0;
}

例外捕捉: Error: 致命的なエラーが発生しました at main.cpp:25 (risky_operation)

#include <source_location>
#include <string_view>

constexpr bool is_internal_file(const std::source_location& loc = std::source_location::current()) {
    std::string_view file = loc.file_name();
    return file.find("internal_") != std::string_view::npos;
}

// 特定の接頭辞を持つファイル以外からの呼び出しを警告するなどの応用が可能

// 誤った例：これではwrapper内の位置が取得されてしまう
void internal_log(std::source_location loc = std::source_location::current()) { /* ... */ }
void wrapper() { internal_log(); } 

// 正しい例：呼び出し元の情報を伝播させる
void wrapper(std::source_location loc = std::source_location::current()) {
    internal_log(loc); 
}