233 lines
9.5 KiB
Markdown
233 lines
9.5 KiB
Markdown
# Loguru: a lightweight and flexible C++ logging library.
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[](https://ci.appveyor.com/project/emilk/loguru)
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## At a glance
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## Documentation
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Documentation can be found at https://emilk.github.io/loguru/index.html.
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## License
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This software is in the public domain. Where that dedication is not recognized, you are granted a perpetual, irrevocable license to copy, modify and distribute it as you see fit.
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That being said, I would appreciate credit!
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If you find Loguru useful, tweet me at @ernerfeldt mail me at emil.ernerfeldt@gmail.com.
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## Why another logging library?
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I have yet to come across a nice, light-weight logging library for C++ that does everything I want. So I made one!
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In particular, I want logging that produces logs that are both human-readable and easily grep:ed. I also want to be able to hook into the logging process to print some of the more severe messages on-screen in my app (for dev-purposes).
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## Features:
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* Simple integration
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* Just two files: `loguru.hpp` and `loguru.cpp`.
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* Either build and link `loguru.cpp` or just `#include <loguru.cpp>` in one of your own .cpp files.
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* Small, simple library.
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* Small header with no `#include`s for **fast compile times** (see separate heading).
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* No dependencies.
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* Cross-platform
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* Flexible:
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* User can install callbacks for logging (e.g. to draw log messages on screen in a game).
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* User can install callbacks for fatal error (e.g. to pause an attached debugger or throw an exception).
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* Support multiple file outputs, either trunc or append:
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* e.g. a logfile with just the latest run at low verbosity (high readability).
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* e.g. a full logfile at highest verbosity which is appended to on every run.
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* Full featured:
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* Verbosity levels.
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* Supports assertions: `CHECK_F(fp != nullptr, "Failed to open '%s'", filename)`
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* Supports abort: `ABORT_F("Something went wrong, debug value is %d", value)`.
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* Stack traces printed on abort.
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* Stack traces are cleaned up somewhat.
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* Before cleanup: `some_function_name(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&)`
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* After cleanup: `some_function_name(std::vector<std::string> const&)`
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* Stack traces are printed [the right way](http://yellerapp.com/posts/2015-01-22-upside-down-stacktraces.html):
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* Chronological order with the most relevant at the end.
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* (most) signals writes stack traces.
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* Fast:
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- When configured in unbuffered mode (loguru::g_flush_interval_ms = 0):
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+ 6-8 us when logging to stderr + file (rMBP + SSD + Clang).
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+ About 25%-75% faster than GLOG on my MacBook Pro (Clang).
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+ About the same as GLOG on my Linux Desktop (GCC).
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- With loguru::g_flush_interval_ms set to ~100 ms:
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+ 3-5 us when logging to stderr + file (rMBP + SSD + Clang).
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+ About twice as fast as GLOG.
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* Drop-in replacement for most of GLOG (except for setup code).
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* Choose between using printf-style or std::cout-style formatting.
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* Compile-time checked printf-formating (on supported compilers).
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* Support for [fmtlib](https://github.com/fmtlib/fmt) formatting.
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* Add `#define LOGURU_USE_FMTLIB 1`, before including `loguru.hpp`
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* You also need to set up the `fmtlib` include directory for building as well as linking against `fmtlib`, alternatively use the `FMT_HEADER_ONLY` preprocessor definition.
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* Assertion failures are marked with `noreturn` for the benefit of the static analyzer and optimizer.
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* All logging also written to stderr.
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* With colors on supported terminals.
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* Thread-safe.
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* Can be configured to either:
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* Flush every `loguru::g_flush_interval_ms` in a background thread
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* Flushes output on each call so you won't miss anything even on hard crashes (and still faster than buffered GLOG!).
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* Prefixes each log line with:
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* Date and time to millisecond precision.
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* Application uptime to millisecond precision.
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* Thread name or id (you can set the name with `loguru::set_thread_name`).
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* File and line.
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* Log level.
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* Indentation (see *Scopes*).
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* Error context:
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* Catch the values of local variables and print them only on a crash (see *Error context*).
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* Scopes (see *Scopes*).
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* grep:able logs:
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* Each line has all the info you need (e.g. date).
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* You can easily filter out high verbosity levels after the fact.
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## Compiling
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Just include <loguru.hpp> where you want to use Loguru.
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Then either compile and link with `loguru.cpp` or in one .cpp file: `#include <loguru.cpp>`
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Make sure you compile with `-std=c++11 -lpthread -ldl` on relevant environments.
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## Usage
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``` C++
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#include <loguru.hpp>
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…
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// Optional, but useful to time-stamp the start of the log.
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// Will also detect verbosity level on command line as -v.
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loguru::init(argc, argv);
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// Put every log message in "everything.log":
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loguru::add_file("everything.log", loguru::Append, loguru::Verbosity_MAX);
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// Only log INFO, WARNING, ERROR and FATAL to "latest_readable.log":
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loguru::add_file("latest_readable.log", loguru::Truncate, loguru::Verbosity_INFO);
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// Only show most relevant things on stderr:
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loguru::g_stderr_verbosity = 1;
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LOG_SCOPE_F(INFO, "Will indent all log messages within this scope.");
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LOG_F(INFO, "I'm hungry for some %.3f!", 3.14159);
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LOG_F(2, "Will only show if verbosity is 2 or higher");
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VLOG_F(get_log_level(), "Use vlog for dynamic log level (integer in the range 0-9, inclusive)");
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LOG_IF_F(ERROR, badness, "Will only show if badness happens");
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auto fp = fopen(filename, "r");
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CHECK_F(fp != nullptr, "Failed to open file '%s'", filename);
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CHECK_GT_F(length, 0); // Will print the value of `length` on failure.
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CHECK_EQ_F(a, b, "You can also supply a custom message, like to print something: %d", a + b);
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// Each function also comes with a version prefixed with D for Debug:
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DCHECK_F(expensive_check(x)); // Only checked #if !NDEBUG
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DLOG_F(INFO, "Only written in debug-builds");
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// Turn off writing to stderr:
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loguru::g_stderr_verbosity = loguru::Verbosity_OFF;
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// Turn off writing err/warn in red:
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loguru::g_colorlogtostderr = false;
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// Throw exceptions instead of aborting on CHECK fails:
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loguru::set_fatal_handler([](const loguru::Message& message){
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throw std::runtime_error(std::string(message.prefix) + message.message);
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});
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```
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If you prefer logging with streams:
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``` C++
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#define LOGURU_WITH_STREAMS 1
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#include <loguru.hpp>
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...
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LOG_S(INFO) << "Look at my custom object: " << a.cross(b);
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CHECK_EQ_S(pi, 3.14) << "Maybe it is closer to " << M_PI;
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```
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For more info, see [the official documentation](https://emilk.github.io/loguru/index.html).
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## Grep:able logs
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``` bash
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# Only show warnings, errors and fatal messages:
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cat logfile.txt | egrep "[^0-9]\|"
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# Ignore verbosity-levels 4 and above:
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cat logfile.txt | egrep "[^4-9]\|"
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# Only show verbosity-level 6:
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cat logfile.txt | egrep "6\|"
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# Only show messages from the main thread:
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cat logfile.txt | egrep "\[main thread \]"
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```
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## No includes in loguru.hpp
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I abhor logging libraries that `#include`'s everything from `iostream` to `windows.h` into every compilation unit in your project. Logging should be frequent in your source code, and thus as lightweight as possible. Loguru's header has *no #includes*. This means it will not slow down the compilation of your project.
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In a test of a medium-sized project, including `loguru.hpp` instead of `glog/logging.hpp` everywhere gave about 10% speedup in compilation times.
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Note, however, that this gives you the bare-bones version of Loguru with printf-style logging. If you want `std::ostream` style logging (or GLOG functionality) you need to `#define LOGURU_WITH_STREAMS 1` before `#include <loguru.hpp>`, and that will make `loguru.hpp` include `<sstream>`. No away around it!
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## Scopes
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The library supports scopes for indenting the log-file. Here's an example:
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``` C++
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int main(int argc, char* argv[])
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{
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loguru::init(argc, argv);
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LOG_SCOPE_FUNCTION(INFO);
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LOG_F(INFO, "Doing some stuff...");
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for (int i=0; i<2; ++i) {
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VLOG_SCOPE_F(1, "Iteration %d", i);
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auto result = some_expensive_operation();
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LOG_IF_F(WARNING, result == BAD, "Bad result");
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}
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LOG_F(INFO, "Time to go!");
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return 0;
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}
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```
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This will output:
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```
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loguru.cpp:184 0| arguments: ./loguru_test test -v1
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loguru.cpp:185 0| Verbosity level: 1
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loguru.cpp:186 0| -----------------------------------
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loguru_test.cpp:108 0| { int main_test(int, char **)
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loguru_test.cpp:109 0| . Doing some stuff...
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loguru_test.cpp:111 1| . { Iteration 0
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loguru_test.cpp:111 1| . } 0.133 s: Iteration 0
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loguru_test.cpp:111 1| . { Iteration 1
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loguru_test.cpp:113 0| . . Bad result
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loguru_test.cpp:111 1| . } 0.134 s: Iteration 1
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loguru_test.cpp:115 0| . Time to go!
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loguru_test.cpp:108 0| } 0.267 s: int main_test(int, char **)
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```
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# `ERROR_CONTEXT`
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You can also optionally log things ONLY if there is a crash. This is a very useful feature:
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```
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void process_file(const char* filename)
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{
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ERROR_CONTEXT("filename", filename);
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parse_file(filename); // Only if this crashes will filename be logged.
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}
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```
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## Streams vs printf
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Some logging libraries only supports stream style logging, not printf-style. This means that what in Loguru is:
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``` C++
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LOG_F(INFO, "Some float: %+05.3f", number);
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```
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in Glog becomes something along the lines of:
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``` C++
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LOG(INFO) << "Some float: " << std::setfill('0') << std::setw(5) << std::setprecision(3) << number;
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```
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Loguru allows you to use whatever style you prefer.
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