A lightweight C++ logging library
UNLICENSE License
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).
loguru.hpp
and loguru.cpp
.loguru.cpp
or just #include <loguru.cpp>
in one of your own .cpp files.#include
s for fast compile times (see separate heading).CHECK_F(fp != nullptr, "Failed to open '%s'", filename)
ABORT_F("Something went wrong, debug value is %d", value)
.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&)
some_function_name(std::vector<std::string> const&)
#define LOGURU_USE_FMTLIB 1
, before including loguru.hpp
fmtlib
include directory for building as well as linking against fmtlib
, alternatively use the FMT_HEADER_ONLY
preprocessor definition.noreturn
for the benefit of the static analyzer and optimizer.loguru::g_flush_interval_ms
in a background threadloguru::set_thread_name
).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>
…
// 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 **)
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.
}
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.