Introduction

pml_log is a simple thread safe logging library for C++

Dependencies

The library uses moodycamel::concurrentqueue

If you build the library using cmake then this repo will be cloned automatically for you.

Compiling

The library uses cmake to handle fetching the required dependencies and configuring the build. There are the following custom cmake variables used to define the location to clone the dependenies to

• DIR_BASE (default: the root directory of log/external) the base location for the external libraries
• DIR_QUEUE (default: DIR_BASE/concurrentqueue) the location of concurrentqueue

How it works

The library consists of two public classes Stream and Output and an internal class Manager

The Stream class contains a std::stringstream and a log level variable. When a Stream is flushed, either by the program passing std::endl; or in the Stream destructor, the contents of the stream are added to a queue in the Manager class.

The Manager class runs is a separate thread and has a simple loop to handle the log messages added to the queue. It send each message to all the defined Output objects.

The Output class defines what should be done with the log message. The base class checks whether the level of the log message exceeds a configured minimum level and if so outputs the message to std::cout.

There is also a File class derived from the base Output class that saves the message to a file.

It is possible for the developer to derive their own Output classes to handle log messages in other ways.

Usage

At the start of your program you should assign one or more output objects to the Manager

// Output log messages to console
auto nOutputId = pml::log::Stream::AddOutput(std::make_unique<pml::log::Output>());
//Output log messages to files
auto nFileId = pml::log::Stream::AddOutput(std::make_unique<pml::log::File>("/var/log/myprog));

To create a log message you can simply call the helper functions

pml::log::info("myprog") << "This is an info message";
pml::log::debug("myprog") << "And this is a debug message";

You can also create a Stream object and keep adding to the log message to it

auto stream = pml::log::Stream(pml::log::Level::kWarning, "myprog");
stream << "This is the start of my very long warning log \n";
...
stream << "and this is the end of my log message";

To decide what log messages get displayed on the console, saved to file etc you can set the minimum Level of log message to display. The levels are

• pml::log::Level::kTrace
• pml::log::Level::kDebug
• pml::log::Level::kInfo
• pml::log::Level::kWarning
• pml::log::Level::kError
• pml::log::Level::kCritical

//Set minimum output level for all outputs to be kInfo
pml:log::Stream::SetOutputLevel(pml::log::Level::kInfo);

//set the minimum output level for the console output to be kTrace
pml::log::Stream::SetOutputLevel(nOutputId, pml::log::Level::kTrace);

Before your application exits you must stop the Manager thread

// stop logging thread cleanly
pml::log::Stream::Stop();
return 0;