Adding so lib to cmake

[szy1210]

Beside libogg.a, libogg.so is generated by modifying file CMakeLists.txt

[willson-chen]

It works on Ubuntu 18.04.3 LTS with x86_64

[willson-chen]

Also works on win10 with VS2019

[rillian]

@evpobr Would you mind reviewing this, please?

[evpobr]

@willson-chen , what's wrong with standard BUILD_SHARED_LIBS option?

[willson-chen]

Cmake generates dynamic lib or static lib according to configurations. This is not wrong but not so convenient for libogg users. Referring to automake which generates dynamic lib and static lib at the same time, I think it is reasonable to make cmake work as the same way. What do you think of it? @rillian @evpobr

[willson-chen]

@evpobr , your comment reminded me about the option. If run cmake with BUILD_SHARED_LIBS, no static lib would be generated. @szy1210

[evpobr]

Benefits

• You can build static/shared library at once.

Disadvantages

• Duplicated and overbloated code. You need options to control two targets (BUILD_SHARED_LIBS and BUILD_STATIC_LIBS) and add logic to prevent user to disable both of them. If some application uses libary in your project you need to add options to contol which library type must be linked to application and add code to detect wrong option combinations.

• Not all plaftorms supports both static/shared libraries. By default CMake with select supported library type, but with separated library targets configuration will fail. Or you need add logic to detect it.

• You don't need to build both static/shared builds at the same time very often. If you need it, you can always build and install static and shared libraries using different build directories:

  mkdir cmake-build-shared
  cd cmake-build-shared
  cmake .. -DBUILD_SHARED_LIBS=ON -D -DCMAKE_INSTALL_PREFIX=<SHARED_LIB_PATH>
  cmake --build . --config Debug --target INSTALL
  mkdir cmake-build-static
  cd cmake-build-static
  cmake .. -DBUILD_SHARED_LIBS=OFF -D -DCMAKE_INSTALL_PREFIX=<STATIC_LIB_PATH>
  cmake --build . --config Debug --target INSTALL
  

  After that use Ogg_DIR variable to set path to required build:

  cmake .. -DOgg_DIR=<SHARED_LIB_PATH>
  

  or

  cmake .. -DOgg_DIR=<STATIC_LIB_PATH>
  

  Or even better - you can use package manager to do it: Vcpkg, Conan etc.

  With Vcpkg:

  vcpkg install libogg:x64-windows
  vcpkg install libogg:x64-windows-static
  cmake .. -DVCPKG_TARGET_TRIPLET=x64-windows -DCMAKE_TOOLCHAIN_FILE=%VCPKG_ROOT%\scripts\buildsystems\vcpkg.cmake 
  cmake .. -DVCPKG_TARGET_TRIPLET=x64-windows-static -DCMAKE_TOOLCHAIN_FILE=%VCPKG_ROOT%\scripts\buildsystems\vcpkg.cmake 
  

[szy1210]

Thank you both @evpobr @willson-chen

[willson-chen]

@evpobr , I have to raise my hat to you. I need to learn more about cmake.