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126 lines
3.4 KiB
Plaintext
126 lines
3.4 KiB
Plaintext
= Shared Library
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:toc:
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:toc-placement!:
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toc::[]
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# Introduction
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Shows a hello world example which first creates and links a shared library.
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This also shows how to create an link:https://cmake.org/cmake/help/v3.0/manual/cmake-buildsystem.7.html#alias-targets[alias target]
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The files in this tutorial are below:
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```
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$ tree
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.
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├── CMakeLists.txt
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├── include
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│ └── shared
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│ └── Hello.h
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└── src
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├── Hello.cpp
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└── main.cpp
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```
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* link:CMakeLists.txt[] - Contains the CMake commands you wish to run
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* link:include/shared/Hello.h[] - The header file to include
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* link:src/Hello.cpp[] - A source file to compile
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* link:src/main.cpp[] - The source file with main
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# Concepts
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## Adding a Shared Library
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As with the previous example on static libraries, the +add_library()+ function
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is also used to create a shared library from some source files.
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This is called as follows:
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[source,cmake]
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----
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add_library(hello_library SHARED
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src/Hello.cpp
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)
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----
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This will be used to create a shared library with the name libhello_library.so with
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the sources passed to the +add_library()+ function.
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## Alias Target
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As the name suggests an link:https://cmake.org/cmake/help/v3.0/manual/cmake-buildsystem.7.html#alias-targets[alias target] is an alternative name for a target that can be used instead of the real target name in read-only contexts.
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[source,cmake]
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----
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add_library(hello::library ALIAS hello_library)
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----
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As shown below, this allows you to reference the target using the alias name when linking it against other targets.
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## Linking a Shared Library
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Linking a shared library is the same as linking a static library. When creating your
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executable use the the +target_link_library()+ function to point to your library
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[source,cmake]
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----
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add_executable(hello_binary
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src/main.cpp
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)
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target_link_libraries(hello_binary
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PRIVATE
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hello::library
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)
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----
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This tells CMake to link the hello_library against the hello_binary executable using the alias target name.
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An example of this being called by the linker is
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```
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/usr/bin/c++ CMakeFiles/hello_binary.dir/src/main.cpp.o -o hello_binary -rdynamic libhello_library.so -Wl,-rpath,/home/matrim/workspace/cmake-examples/01-basic/D-shared-library/build
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```
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# Building the Example
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[source,bash]
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----
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$ mkdir build
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$ cd build
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$ cmake ..
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-- The C compiler identification is GNU 4.8.4
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-- The CXX compiler identification is GNU 4.8.4
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-- Check for working C compiler: /usr/bin/cc
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-- Check for working C compiler: /usr/bin/cc -- works
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-- Detecting C compiler ABI info
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-- Detecting C compiler ABI info - done
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-- Check for working CXX compiler: /usr/bin/c++
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-- Check for working CXX compiler: /usr/bin/c++ -- works
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-- Detecting CXX compiler ABI info
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-- Detecting CXX compiler ABI info - done
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-- Configuring done
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-- Generating done
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-- Build files have been written to: /home/matrim/workspace/cmake-examples/01-basic/D-shared-library/build
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$ make
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Scanning dependencies of target hello_library
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[ 50%] Building CXX object CMakeFiles/hello_library.dir/src/Hello.cpp.o
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Linking CXX shared library libhello_library.so
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[ 50%] Built target hello_library
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Scanning dependencies of target hello_binary
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[100%] Building CXX object CMakeFiles/hello_binary.dir/src/main.cpp.o
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Linking CXX executable hello_binary
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[100%] Built target hello_binary
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$ ls
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CMakeCache.txt CMakeFiles cmake_install.cmake hello_binary libhello_library.so Makefile
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$ ./hello_binary
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Hello Shared Library!
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----
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