Documentation can be found at https://emilk.github.io/loguru/index.html.
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.
That being said, I would appreciate credit! If you find Loguru useful, tweet me at @ernerfeldt mail me at [email protected].
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).
- Simple integration
- Just two files:
loguru.hppandloguru.cpp. - Either build and link
loguru.cppor just#include <loguru.cpp>in one of your own .cpp files.
- Just two files:
- Small, simple library.
- Small header with no
#includes for fast compile times (see separate heading). - No dependencies.
- Cross-platform
- Small header with no
- 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&)
- Before cleanup:
- Stack traces are printed the right way:
- Chronological order with the most relevant at the end.
- Stack traces are cleaned up somewhat.
- (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.
- When configured in unbuffered mode (loguru::g_flush_interval_ms = 0):
- 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 includingloguru.hpp - You also need to set up the
fmtlibinclude directory for building as well as linking againstfmtlib, alternatively use theFMT_HEADER_ONLYpreprocessor definition.
- Add
- Assertion failures are marked with
noreturnfor 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_msin a background thread - Flushes output on each call so you won't miss anything even on hard crashes (and still faster than buffered GLOG!).
- Flush every
- 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.
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.
Loguru can be added to an existing CMake project in three ways
add_subdirectory()FetchContent()find_package()
See CMake example for a demonstration.
#include <loguru.hpp>
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// 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:
#define LOGURU_WITH_STREAMS 1
#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.
# 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 "\[main thread \]"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!
The library supports scopes for indenting the log-file. Here's an example:
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 **)
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.
}
Some logging libraries only supports stream style logging, not printf-style. This means that what in Loguru is:
LOG_F(INFO, "Some float: %+05.3f", number);in Glog becomes something along the lines of:
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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