logfmtxx

Header-only C++23 structured logging library using the logfmt format.

Installation

Just copy the include/logfmtxx.hpp in your project.

Or with Shipp, add it to your dependencies:

{
  "name": "myproject",
  "version": "0.1.0",
  "dependencies": [
    {
      "name": "logfmtxx",
      "url": "https://github.com/linkdd/logfmtxx.git",
      "version": "v0.4.0"
    }
  ]
}

Usage

First, include the relevant headers:

#include <iostream> // if you wish to print logs with std::cout or std::cerr
#include <logfmtxx.hpp>

Then create a logger:

auto logger = logfmtxx::logger{
  [](const std::string& message) {
    std::cout << message << std::endl;
  }
};

Or with a functor to avoid allocations:

struct printer {
  void operator()(const std::string& message) {
    std::cout << message << std::endl;
  }
};
auto logger = logfmtxx::logger{printer{}};

Or with global fields:

auto logger = logfmtxx::logger{
  [](const std::string& message) {
    std::cout << message << std::endl;
  },
  logfmtxx::field{"foo", 42},
  logfmtxx::field{"bar", 3.14}
};

Then, call the log() method:

logger.log(logfmtxx::level::info, "hello world");
// or
logger.info("hello world");

The result should be:

time=2001-01-01T00:00:00Z level=info message="hello world" foo=42 bar=3.14000

You can add extra fields as well:

logger.log(
  logfmtxx::level::error,
  "internal server error",
  logfmtxx::field{"http.method", "GET"},
  logfmtxx::field{"http.path", "/"},
  logfmtxx::field{"http.status", 500}
);

The result should be:

time=2001-01-01T00:00:00Z level=error message="internal server error" foo=42 bar=3.14000 http.method="GET" http.path="/" http.status=500

If your type implements as_string(), it can be used with a field:

struct foo {
  std::string as_string() const {
    return "i am foo";
  }
};

logger.log(logfmtxx::level::info, "example", logfmtxx::field{"foo", foo{}});

Benchmark

CPU: 13th Gen Intel(R) Core(TM) i7-13700K 3.40 GHz

Results:

ns/op	op/s	err%	total	benchmark
7,326.07	136,498.88	1.1%	0.09	logger.info with context (fast)
7,169.35	139,482.70	0.7%	0.09	logger.info without context (fast)
9,707.22	103,016.06	1.3%	0.03	logger.info with context (slow)
9,448.67	105,835.01	0.7%	0.03	logger.info without context (slow)

License

This software is released under the terms of the BSD 0-clause License.