Commit fab48cf1 authored by Kitware Robot's avatar Kitware Robot Committed by Utkarsh Ayachit

loguru 2019-01-29 (6fd7dea9)

Code extracted from:

at commit 6fd7dea9d3dbbb797af0d981fa16143556b739a7 (for/vtk).
# XXX(kitware): Ignore whitespace issues.
* -whitespace
SOURCES ${sources}
HEADERS ${headers}
HEADERS_SUBDIR "vtkloguru")
EXPORT_FILE_NAME vtkloguru_export.h)
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.
That being said, I would appreciate credit! If you find Loguru useful, tweet me
at @ernerfeldt mail me at
# loguru fork for VTK
This branch contains chanegs required to embed loguru into VTK. This includes
changes made primarily to the build system to allow it to be embedded into
another source tree as well as a header to facilitate mangling of the symbols to
avoid conflicts with other copies of the library within a single process.
* ignore whitespace issues
* integreate with VTK's module system
* mangle `loguru` namespace to `vtkloguru`
* add license
# Loguru: a lightweight and flexible C++ logging library.
[![Build status](](
## At a glance
![Loguru terminal output](docs/terminal_colors.png)
## Documentation
Documentation can be found at
## License
This software is in the public domain. Where that dedication is not recognized, you are granted a perpetual, irrevocable license to copy and modify this file as you see fit.
That being said, I would appreciate credit!
If you find Loguru useful, tweet me at @ernerfeldt mail me at
## 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 <loguru.cpp>` 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::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&)`
* After cleanup: `some_function_name(std::vector<std::string> const&)`
* Stack traces are printed [the right way](
* 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]( 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 <loguru.hpp> where you want to use Loguru.
Then either compile and link with `loguru.cpp` or in one .cpp file: `#include <loguru.cpp>`
Make sure you compile with `-std=c++11 -lpthread -ldl` on relevant environments.
## Usage
``` C++
#include <loguru.hpp>
// 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++
#include <loguru.hpp>
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](
## 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 <loguru.hpp>`, and that will make `loguru.hpp` include `<sstream>`. 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_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 **)
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.
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