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https://github.com/emilk/loguru
A lightweight C++ logging library
https://github.com/emilk/loguru
Last synced: 25 days ago
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A lightweight C++ logging library
- Host: GitHub
- URL: https://github.com/emilk/loguru
- Owner: emilk
- License: unlicense
- Created: 2015-03-22T17:45:23.000Z (over 9 years ago)
- Default Branch: master
- Last Pushed: 2024-07-01T07:58:15.000Z (4 months ago)
- Last Synced: 2024-09-27T04:41:15.942Z (about 1 month ago)
- Language: C++
- Size: 981 KB
- Stars: 1,769
- Watchers: 56
- Forks: 257
- Open Issues: 84
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- AwesomeCppGameDev - loguru
README
# Loguru: a lightweight and flexible C++ logging library.
[](https://ci.appveyor.com/project/emilk/loguru)
## At a glance
## Documentation
Documentation can be found at https://emilk.github.io/loguru/index.html.
## License
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.
Loguru is also available under [The Unlicense](https://choosealicense.com/licenses/unlicense/).
That being said, I would appreciate credit!
If you find Loguru useful, tweet me at @ernerfeldt mail me at [email protected].
## Why another logging library?
I have yet to come across a nice, light-weight logging library for C++ that does everything I want. So I made one!
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).
## Features:
* Simple integration
* Just two files: `loguru.hpp` and `loguru.cpp`.
* Either build and link `loguru.cpp` or just `#include ` in one of your own .cpp files.
* Small, simple library.
* Small header with no `#include`s for **fast compile times** (see separate heading).
* No dependencies.
* Cross-platform
* Flexible:
* User can install callbacks for logging (e.g. to draw log messages on screen in a game).
* User can install callbacks for fatal error (e.g. to pause an attached debugger or throw an exception).
* Support multiple file outputs, either trunc or append:
* e.g. a logfile with just the latest run at low verbosity (high readability).
* e.g. a full logfile at highest verbosity which is appended to on every run.
* Full featured:
* Verbosity levels.
* Supports assertions: `CHECK_F(fp != nullptr, "Failed to open '%s'", filename)`
* Supports abort: `ABORT_F("Something went wrong, debug value is %d", value)`.
* Stack traces printed on abort.
* Stack traces are cleaned up somewhat.
* Before cleanup: `some_function_name(std::__1::vector, std::__1::allocator >, std::__1::allocator, std::__1::allocator > > > const&)`
* After cleanup: `some_function_name(std::vector const&)`
* Stack traces are printed [the right way](http://yellerapp.com/posts/2015-01-22-upside-down-stacktraces.html):
* Chronological order with the most relevant at the end.
* (most) signals writes stack traces.
* Fast:
- When configured in unbuffered mode (loguru::g_flush_interval_ms = 0):
+ 6-8 us when logging to stderr + file (rMBP + SSD + Clang).
+ About 25%-75% faster than GLOG on my MacBook Pro (Clang).
+ About the same as GLOG on my Linux Desktop (GCC).
- With loguru::g_flush_interval_ms set to ~100 ms:
+ 3-5 us when logging to stderr + file (rMBP + SSD + Clang).
+ About twice as fast as GLOG.
* Drop-in replacement for most of GLOG (except for setup code).
* Choose between using printf-style or std::cout-style formatting.
* Compile-time checked printf-formating (on supported compilers).
* Support for [fmtlib](https://github.com/fmtlib/fmt) formatting.
* Add `#define LOGURU_USE_FMTLIB 1`, before including `loguru.hpp`
* 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.
* Assertion failures are marked with `noreturn` for the benefit of the static analyzer and optimizer.
* All logging also written to stderr.
* With colors on supported terminals.
* Thread-safe.
* Can be configured to either:
* Flush every `loguru::g_flush_interval_ms` in a background thread
* Flushes output on each call so you won't miss anything even on hard crashes (and still faster than buffered GLOG!).
* Prefixes each log line with:
* Date and time to millisecond precision.
* Application uptime to millisecond precision.
* Thread name or id (you can set the name with `loguru::set_thread_name`).
* File and line.
* Log level.
* Indentation (see *Scopes*).
* Error context:
* Catch the values of local variables and print them only on a crash (see *Error context*).
* Scopes (see *Scopes*).
* grep:able logs:
* Each line has all the info you need (e.g. date).
* You can easily filter out high verbosity levels after the fact.
## Compiling
Just include where you want to use Loguru.
Then either compile and link with `loguru.cpp` or in one .cpp file: `#include `
Make sure you compile with `-std=c++11 -lpthread -ldl` on relevant environments.
## CMake Instructions
Loguru can be added to an existing CMake project in three ways
1. `add_subdirectory()`
2. `FetchContent()`
3. `find_package()`
See [CMake example](./loguru_cmake_example/CMakeLists.txt) for a demonstration.
## Usage
``` C++
#include
…
// Optional, but useful to time-stamp the start of the log.
// Will also detect verbosity level on command line as -v.
loguru::init(argc, argv);
// Put every log message in "everything.log":
loguru::add_file("everything.log", loguru::Append, loguru::Verbosity_MAX);
// Only log INFO, WARNING, ERROR and FATAL to "latest_readable.log":
loguru::add_file("latest_readable.log", loguru::Truncate, loguru::Verbosity_INFO);
// Only show most relevant things on stderr:
loguru::g_stderr_verbosity = 1;
LOG_SCOPE_F(INFO, "Will indent all log messages within this scope.");
LOG_F(INFO, "I'm hungry for some %.3f!", 3.14159);
LOG_F(2, "Will only show if verbosity is 2 or higher");
VLOG_F(get_log_level(), "Use vlog for dynamic log level (integer in the range 0-9, inclusive)");
LOG_IF_F(ERROR, badness, "Will only show if badness happens");
auto fp = fopen(filename, "r");
CHECK_F(fp != nullptr, "Failed to open file '%s'", filename);
CHECK_GT_F(length, 0); // Will print the value of `length` on failure.
CHECK_EQ_F(a, b, "You can also supply a custom message, like to print something: %d", a + b);
// Each function also comes with a version prefixed with D for Debug:
DCHECK_F(expensive_check(x)); // Only checked #if !NDEBUG
DLOG_F(INFO, "Only written in debug-builds");
// Turn off writing to stderr:
loguru::g_stderr_verbosity = loguru::Verbosity_OFF;
// Turn off writing err/warn in red:
loguru::g_colorlogtostderr = false;
// Throw exceptions instead of aborting on CHECK fails:
loguru::set_fatal_handler([](const loguru::Message& message){
throw std::runtime_error(std::string(message.prefix) + message.message);
});
```
If you prefer logging with streams:
``` C++
#define LOGURU_WITH_STREAMS 1
#include
...
LOG_S(INFO) << "Look at my custom object: " << a.cross(b);
CHECK_EQ_S(pi, 3.14) << "Maybe it is closer to " << M_PI;
```
For more info, see [the official documentation](https://emilk.github.io/loguru/index.html).
## Grep:able logs
``` bash
# Only show warnings, errors and fatal messages:
cat logfile.txt | egrep "[^0-9]\|"
# Ignore verbosity-levels 4 and above:
cat logfile.txt | egrep "[^4-9]\|"
# Only show verbosity-level 6:
cat logfile.txt | egrep "6\|"
# Only show messages from the main thread:
cat logfile.txt | egrep "\[main thread \]"
```
## No includes in loguru.hpp
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.
In a test of a medium-sized project, including `loguru.hpp` instead of `glog/logging.hpp` everywhere gave about 10% speedup in compilation times.
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 `, and that will make `loguru.hpp` include ``. No away around it!
## Scopes
The library supports scopes for indenting the log-file. Here's an example:
``` C++
int main(int argc, char* argv[])
{
loguru::init(argc, argv);
LOG_SCOPE_FUNCTION(INFO);
LOG_F(INFO, "Doing some stuff...");
for (int i=0; i<2; ++i) {
VLOG_SCOPE_F(1, "Iteration %d", i);
auto result = some_expensive_operation();
LOG_IF_F(WARNING, result == BAD, "Bad result");
}
LOG_F(INFO, "Time to go!");
return 0;
}
```
This will output:
```
loguru.cpp:184 0| arguments: ./loguru_test test -v1
loguru.cpp:185 0| Verbosity level: 1
loguru.cpp:186 0| -----------------------------------
loguru_test.cpp:108 0| { int main_test(int, char **)
loguru_test.cpp:109 0| . Doing some stuff...
loguru_test.cpp:111 1| . { Iteration 0
loguru_test.cpp:111 1| . } 0.133 s: Iteration 0
loguru_test.cpp:111 1| . { Iteration 1
loguru_test.cpp:113 0| . . Bad result
loguru_test.cpp:111 1| . } 0.134 s: Iteration 1
loguru_test.cpp:115 0| . Time to go!
loguru_test.cpp:108 0| } 0.267 s: int main_test(int, char **)
```
# `ERROR_CONTEXT`
You can also optionally log things ONLY if there is a crash. This is a very useful feature:
```
void process_file(const char* filename)
{
ERROR_CONTEXT("filename", filename);
parse_file(filename); // Only if this crashes will filename be logged.
}
```
## Streams vs printf
Some logging libraries only supports stream style logging, not printf-style. This means that what in Loguru is:
``` C++
LOG_F(INFO, "Some float: %+05.3f", number);
```
in Glog becomes something along the lines of:
``` C++
LOG(INFO) << "Some float: " << std::setfill('0') << std::setw(5) << std::setprecision(3) << number;
```
Loguru allows you to use whatever style you prefer.