Easylogging++ Documentation

The samples/STL/shared-static-libs/ directory provides a demonstration of how to compile applications using both shared and static libraries with easylogging++.

The project structure consists of:

• compile_shared.sh: Script for shared library compilation.
• compile_static.sh: Script for static library compilation.
• lib/include/: Contains easylogging++.h and a custom header mylib.hpp.
• lib/mylib.cpp: Implementation of the custom library.
• myapp.cpp: The main application entry point.

To use Easylogging++ in your project, follow these steps:

1. Download the latest version.
2. Include easylogging++.h and easylogging++.cc in your project.
3. Initialize the library using the INITIALIZE_EASYLOGGINGPP macro. This macro must be used exactly once per application (typically in the file containing main) to avoid compilation errors involving extern variables.
4. Use the LOG(LEVEL) macro to record messages.

Note on C++ Versions: If your application does not support C++11, use version v8.91, which is stable for C++98 and C++03.

#include "easylogging++.h"

INITIALIZE_EASYLOGGINGPP

int main(int argc, char* argv[]) {
   LOG(INFO) << "My first info log using default logger";
   return 0;
}

You can use a single file to register new loggers and configure existing ones. In this file, logger IDs are prefixed with two dashes (--).

Global Configuration File Format:

-- LOGGER_ID_1
  CONFIGURATION_KEY = "VALUE"

-- LOGGER_ID_2
  CONFIGURATION_KEY = "VALUE"

Use el::Loggers::configureFromGlobal("filename.conf") to apply this file.

int main(void) {
   // Registers new and configures it or
   // configures existing logger - everything in global.conf
   el::Loggers::configureFromGlobal("global.conf");
   // .. Your prog
   return 0;
}

When compiling your application, ensure you include easylogging++.cc in your compilation command and specify the C++11 standard (or higher) if using the latest version.

g++ main.cc easylogging++.cc -o prog -std=c++11

You can use the vcpkg dependency manager to install Easylogging++.

git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh
./vcpkg integrate install
./vcpkg install easyloggingpp

Easylogging++ provides macros to log only when specific conditions are met or after a certain number of hits.

Conditional Logging (ends in _IF):

• LOG_IF(condition, LEVEL)
• CLOG_IF(condition, LEVEL, logger ID)

Occasional Logging (hit-count based):

• LOG_EVERY_N(n, LEVEL): Logs every $n$ hits.
• LOG_AFTER_N(n, LEVEL): Only logs after $n$ hits have occurred.
• LOG_N_TIMES(n, LEVEL): Logs exactly $n$ times.

Note: For debug-only mode, prefix these macros with D (e.g., DLOG_IF, DLOG_EVERY_N).

// Conditional
LOG_IF(condition, INFO) << "Logged if condition is true";

// Occasional
for (int i = 1; i <= 10; ++i) {
   LOG_EVERY_N(2, INFO) << "Logged every second iter";
}

for (int i = 1; i <= 10; ++i) {
   LOG_AFTER_N(2, INFO) << "Log after 2 hits; " << i;
}

for (int i = 1; i <= 100; ++i) {
   LOG_N_TIMES(3, INFO) << "Log only 3 times; " << i;
}

To install Easylogging++ system-wide using CMake, use the following commands. You can enable specific options using -D<option>=ON:

• lib_utc_datetime: Defines ELPP_UTC_DATETIME.
• build_static_lib: Builds a static library for Easylogging++.

Note: Even when installing via CMake, you still need the easylogging++.cc file in your project to compile.

mkdir build
cd build
cmake -Dtest=ON ../
make
make test
make install