yalo

Yet Another Logger: C++ light-weight logger

Features

• Single header file, less than 1,000 lines of code
• Supports C++11 and later
• Supports Linux, macOS, and Windows
• Threadsafe (and thread identification)
• Minimal coding to log
• Logs timestamp, thread, level, file, line number, function, condition
• Logs to stdout, stderr, and/or files
• Customize to log to other destinations
• Customize to change the format of the logging output
• Can create/update a file to change logging settings while code is running
• Can automaticaly log all if, while, and switch statements in Trace mode
• Can set logging level per file or group of files
• Over 80% unit test code coverage

Logging Levels

Constant	Call	Description
yalo::Fatal	lFatal	Always log and call abort()
yalo::Fatal	lFatalIf(condition)	If condition is true, log and call abort()
yalo::Log	lLog	Information that should always be in the log (version, settings, etc)
yalo::Error	lError	An error occurred (default logging level)
yalo::Error	lErrorIf(condition)	condition is the error condition and will log if true(default logging level)
yalo::Warning	lWarn	Warn about potential problems
yalo::Warning	lWarnIf(condition)	condition is a potential problem if true
yalo::Info	lInfo	Log general information
yalo::Debug	lDebug	Log information helpful for debugging
yalo::Verbose	lVerbose	Log an excessive amount of information for deeper debugging
yalo::Trace	lTrace	Log execution, including every if, while, and switch

Trace if, while, and switch

By default, every if, while, and switch will be available in yalo::Trace mode. This adds a small amount of code to every if, while iteration, and switch. While this code is small, it may have a performance impact. To disable this tracing ability, you can define DISABLE_YALO_TRACE.

Example logging code

    lLog << "Program version" << version_string;
    lErr << "We're all going to die!";
    lErrIf(file == nullptr) << "crash eminent!";
    lWarn << "Warning!";
    lWarnIf(size > 5) << "We should work but this is kind of big" << size;
    lInfo << "How did we get here?";
    lDebug << "iteration #" << iteration << "size = " << size;
    lVerbose << "Checking if we should move forward";
    lTrace << "Here";
    if (x == 5 && y == 7) {...}

Example log

The log can output the following information:

• Timestamp (local or GMT)
• Thread index (index of the order in which the threads logged)
• Log level
• Source file
• Source line number
• Function or method
• Conditional that triggered the logging
• The log message

[2025-02-23 02:52:22.912 (Sun)][0][LOG] New Settings File: bin/testCommandFile.txt
[2025-02-23 02:52:22.912 (Sun)][0][LOG] Resetting format to default GMT
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Resetting format to default
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Adding sink to bin/testCommandFile.log
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] resetLevels to 0
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Turned padding on
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Turned padding off
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Set level #1 pattern = ''
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] Set level #4 pattern = 'test_yalo.cpp'
[2025-02-22 20:52:22.912 -0600 (Sat)][0][DBG][src/tests/test_yalo.cpp:495][testCommandFile] testing
[2025-02-22 20:52:22.912 -0600 (Sat)][0][LOG] New Settings File: bin/nonexistant/path/testCommandFile.txt
[2025-02-23 02:52:22.912 (Sun)][0][WRN][src/tests/test_yalo.cpp:523][testConditionals][value1 > 2] too big
[2025-02-23 02:52:22.912 (Sun)][0][ERR][src/tests/test_yalo.cpp:524][testConditionals][value1 < 10] too small
[2025-02-23 02:52:22.913 (Sun)][0][LOG] New Settings File: bin/nonexistant/path/testCommandFile.txt

Changing log levels at Runtime

In the code you can specify a path to a file to watch for logging settings. You can do this by calling yalo::Logger::setSettingsFile({path}, {secondsBetweenChecks});

Here is an example of the file:

setLevel: Error
setLevel: Trace=main.cpp
addSinkStdErr
addSink:debugging.txt

You can have the following commands in the file:

• addSink
• addSinkStdErr
• addSinkStdOut
• clearSinks
• noPad
• pad
• resetLevels
• setFormatDefault
• setFormatDefaultGMT
• setLevel (globally and for specific files)

addSink

Same as calling Logger::addSink(std::unique_ptr<FileSink>(new FileSink({path})));

addSink:{path}

Starts logging to the given path.

addSinkStdErr

Same as calling Logger::addSink(std::unique_ptr<StdErrSink>(new StdErrSink()));

addSinkStdErr

Starts logging to stderr.

Note: If you are already logging to stderr or specify this command more than once you will see duplicate lines.

addSinkStdOut

Same as calling Logger::addSink(std::unique_ptr<StdOutSink>(new StdOutSink()));

addSinkStdOut

Starts logging to stdout.

Note: If you are already logging to stdout or specify this command more than once you will see duplicate lines.

clearSinks

Same as calling Logger::clearSinks();

clearSinks

Removes all current logging sinks.

Note: If this is not immedeately followed by addSinkStdOut, addSinkStdErr, or addSink then addSinkStdErr will automatically happen.

noPad

Same as calling Logger::setInserterSpacing(InserterAsIs);

noPad

When log streaming, no extra spacing will be inserted between inserts.

lLog << "test" << 5 << "more";

will result in logging:

test5more

pad

Same as calling Logger::setInserterSpacing(InserterPad);

pad

When log streaming, an extra space will be inserted between inserts.

lLog << "test" << 5 << "more";

will result in logging:

test 5 more

resetLevels

Same as calling Logger::resetLevels(_fromString({level}));

resetLevels:{level}

Clears all file pattern files and sets all logging to {level}.

setFormatDefault

Same as calling Logger::setFormat(std::unique_ptr<DefaultFormatter>(new DefaultFormatter()));

setFormatDefault

Reset the log formatter back to the default, using local time.

setFormatDefaultGMT

Same as calling Logger::setFormat(std::unique_ptr<DefaultFormatter>(new DefaultFormatter(DefaultFormatter::GMT)));

setFormatDefaultGMT

Reset the log formatter back to the default, using GMT time.

setLevel

Same as calling Logger::setLevel({level}, {pattern});

setLevel:{level}
setLevel:{level}={pattern}

The first entry will set the default global {level}. The second entry will set the {level} for the given file pattern.

File Patterns

You can specify a file matching pattern to change the logging level per file or group of files. The pattern consists of case-sensitive substrings to look for in the file, separated by semicolon (;). If a pattern begins with a minus (-) then it will not match that pattern. The evaluation walks through all the patterns with positive patterns being ORed in and negative patterns removing files.

File pattern example

src/;-src/include/;-main.cpp

This is interpreted as: files that contain src/ in them, but do not include src/include and do not include main.cpp.

Basically take your filename and walk through the pattern and add it if at matches a positive and remove it when it matches a negative.

src/;-src/include/;.cpp

This example shows all files under src/, but not files in src/include/, but do include .cpp files (including those in src/include/).