From e092eccd268f3e372c56db793345086271d78109 Mon Sep 17 00:00:00 2001
From: "Benjamin A. Beasley" <code@musicinmybrain.net>
Date: Sat, 27 Aug 2022 09:16:31 -0400
Subject: [PATCH] Add a build_shared_lib option (fix #484)

Use the major version number as the SOVERSION.
---
 CHANGELOG.md   |  2 ++
 CMakeLists.txt | 29 ++++++++++++++++++++++++-----
 README.md      |  1 +
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 59265222a..dd64ba320 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
 # Change Log
 
 ## [Unreleased]
+### Features
+ * Add a build_shared_library CMake option
 ### Bug Fixes
  * Fix library installation path on Linux distributions that use lib64
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 314c9152f..507e84b68 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,6 +23,7 @@ endmacro()
 
 option(test "Build all tests" OFF)
 option(build_static_lib "Build easyloggingpp as a static library" OFF)
+option(build_shared_lib "Build easyloggingpp as a shared library" OFF)
 option(lib_utc_datetime "Build library with UTC date/time logging" OFF)
 
 set(ELPP_MAJOR_VERSION "9")
@@ -51,20 +52,38 @@ install(FILES ${CMAKE_CURRENT_BINARY_DIR}/easyloggingpp.pc DESTINATION "${ELPP_P
 include(CheckIncludeFileCXX)
 check_include_file_cxx("execinfo.h" HAVE_EXECINFO)
 if (HAVE_EXECINFO)
-	add_definitions(-DHAVE_EXECINFO)
+        add_definitions(-DHAVE_EXECINFO)
 endif()
 
-if (build_static_lib)
+if (build_shared_lib OR build_shared_lib)
         if (lib_utc_datetime)
                 add_definitions(-DELPP_UTC_DATETIME)
         endif()
 
         require_cpp11()
-        add_library(easyloggingpp STATIC src/easylogging++.cc)
-        set_property(TARGET easyloggingpp PROPERTY POSITION_INDEPENDENT_CODE ON)
+endif()
+
+if (build_static_lib)
+        add_library(easyloggingpp_static STATIC src/easylogging++.cc)
+        set_target_properties(easyloggingpp_static PROPERTIES
+            OUTPUT_NAME easyloggingpp
+            POSITION_INDEPENDENT_CODE ON)
+        set_property(TARGET easyloggingpp_static PROPERTY POSITION_INDEPENDENT_CODE ON)
+
+        install(TARGETS
+            easyloggingpp_static
+            ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
+endif()
+if (build_shared_lib)
+        add_library(easyloggingpp_shared SHARED src/easylogging++.cc)
+        set_target_properties(easyloggingpp_shared PROPERTIES
+            OUTPUT_NAME easyloggingpp
+            POSITION_INDEPENDENT_CODE ON
+            SOVERSION "${ELPP_MAJOR_VERSION}"
+            VERSION "${ELPP_MAJOR_VERSION}.${ELPP_MINOR_VERSION}.${ELPP_PATCH_VERSION}")
 
         install(TARGETS
-            easyloggingpp
+            easyloggingpp_shared
             ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
 endif()
 
diff --git a/README.md b/README.md
index ee3e8f3ca..8ca44b24d 100644
--- a/README.md
+++ b/README.md
@@ -192,6 +192,7 @@ Following options are supported by Easylogging++ cmake and you can turn these op
 
  * `lib_utc_datetime` - Defines `ELPP_UTC_DATETIME`
  * `build_static_lib` - Builds static library for Easylogging++
+ * `build_shared_lib` - Builds shared library for Easylogging++
 
 With that said, you will still need `easylogging++.cc` file in order to compile. For header only, please check [v9.89](https://github.com/amrayn/easyloggingpp/releases/tag/9.89) and lower.