C++ spdlog write logs to a file

Question

I made a logger using spdlog which I use all over my program. But I also want to flush everything to a log file when the program is completed. How can I achieve this? I'm new to spdlog and I couldn't find proper documentation suitable for my situation.

Here are my file's:

Log.h:

#pragma once

#include "spdlog/spdlog.h"
#include "spdlog/fmt/ostr.h"

namespace Engine{
    class Log{
    public:
        static void init();
        inline static std::shared_ptr<spdlog::logger>& GetCoreLoger() { return s_CoreLogger; }
        inline static std::shared_ptr<spdlog::logger>& GetClientLogger  () { return s_ClientLogger;}

        // I want something like this:
        void flush_to_file();

    private:
        static std::shared_ptr<spdlog::logger> s_CoreLogger;
        static std::shared_ptr<spdlog::logger> s_ClientLogger;
    };
}



//Client log macros
#define VI_TRACE(...)      ::Engine::Log::GetClientLogger()->trace(__VA_ARGS__)
#define VI_INFO(...)       ::Engine::Log::GetClientLogger()->info(__VA_ARGS__)
#define VI_WARN(...)       ::Engine::Log::GetClientLogger()->warn(__VA_ARGS__)
#define VI_ERROR(...)      ::Engine::Log::GetClientLogger()->error(__VA_ARGS__)

Log.cpp:

#include "spdlog/sinks/stdout_color_sinks.h"

namespace Engine {
    std::shared_ptr<spdlog::logger> Log::s_CoreLogger;
    std::shared_ptr<spdlog::logger> Log::s_ClientLogger;

    void Log::init() {
        spdlog::set_pattern("%^[%T] %n: %v%$");
        s_CoreLogger = spdlog::stdout_color_mt("VIO");
        s_CoreLogger->set_level(spdlog::level::trace);

        s_ClientLogger = spdlog::stdout_color_mt("APP");
        s_ClientLogger->set_level(spdlog::level::trace);
    }

    // This is what I want:
    void Log::flush_to_file(){
       spdlog::write_to_file(); // Something like this
    }
};

I want everything that spdlog have logged so far to be written into the file when I call that function. Is this possible? If so how can I do it?

Both loggers you show log to stdout, so which file are you talking about? Also, I found the [documentation for `spdlog::logger::flush`](https://spdlog.docsforge.com/v1.x/api/spdlog/logger/flush/) in ten seconds. Reading documentation or header files is a core skill that you will need to develop. — Botje, Sep 16 '22 at 11:49
Multi sink is the way to go. Check here https://github.com/gabime/spdlog/blob/v1.x/example/example.cpp#L242 — Manthan Tilva, Sep 16 '22 at 11:49
@Botje I know I saw that, that's why I've said "find proper documentation **suitable for my situation.**". I wasn't sure how to approach the situation, that's the question. — Turgut, Sep 16 '22 at 14:05

score 1 · Answer 1 · answered Dec 29 '22 at 12:34

1

What you probably need it is a multisink logger, a sink for stdout as you already have and a new one to also log to a file.

auto console_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt>();
auto basic_sink = std::make_shared<spdlog::sinks::basic_file_sink_mt>("mylog.log");
std::vector<spdlog::sink_ptr> sinks{console_sink, basic_sink};
auto logger = std::make_shared<spdlog::logger>("main", sinks.begin(), sinks.end());

spdlog::register_logger(logger); //if it would be used in some other place

Your function flush_to_file probably should call

logger->flush();

To see the file content before the logger shutdown or automatic flush, try to add:

logger->flush_on(spdlog::level::info);

answered Dec 29 '22 at 12:34

fcatho

317
2
14

If i have object1.cpp , object2.cpp ,object3.cpp and main.cpp How can I can I lead all logs from main.cpp. – Amarnath Reddy Surapureddy Feb 03 '23 at 04:57
@AMAR By using `register_logger` the logger will be available for the entire process as a singleton. Basically, just call from `get` to retrieve a logger pointer based on the name given as argument during construction, for instance in object1.cpp: `spdlog::get("main")->info("...");` – fcatho Feb 03 '23 at 23:32
Yes I got it Sir, I implemented. but i am not using register_logger. – Amarnath Reddy Surapureddy Feb 14 '23 at 05:12

C++ spdlog write logs to a file

1 Answers1