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creating_execs_and_libs.rst

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Creating Libraries and Executables

In the previous section, we learned the basics about how to create a CMake project with BLT, how to configure the project and how to build and test BLT's built-in third party libraries.

We now move on to creating libraries and executables using two of BLT's core macros: blt_add_library and blt_add_executable.

We begin with a simple executable that calculates pi by numerical integration (example_1). We will then extract that code into a library, which we link into a new executable (example_2).

Example 1: Basic executable

This example is as basic as it gets. After setting up a BLT CMake project, like blank_project in the previous section, we can start using BLT's macros. Creating an executable is as simple as calling the following macro:

.. literalinclude:: tutorial/calc_pi/CMakeLists.txt
   :language: cmake
   :lines: 28-29

This tells CMake to create an executable named example_1 with one source file (example_1.cpp).

You can create this project yourself or you can run the already provided tutorial/calc_pi project. For ease of use, we have combined many examples into this one CMake project. After running the following commands, you will create the executable <build dir>/bin/example_1:

cd <BLT repository/docs/tutorial/calc_pi
mkdir build
cd build
cmake -DBLT_SOURCE_DIR=../../.. ..
make

blt_add_executable

This is one of the core macros that enables BLT to simplify our CMake-based project. It unifies many CMake calls into one easy to use macro. blt_add_executable creates a CMake executable target with the given sources, sets the output directory to <build dir>/bin (unless overridden with the macro parameter OUTPUT_DIR) and handles internal and external dependencies in a greatly simplified manner. There will be more on that in the following section.

Example 2: One library, one executable

This example is a bit more exciting. This time we are creating a library that calculates pi and then linking that library into an executable.

First, we create the library with the following BLT code:

.. literalinclude:: tutorial/calc_pi/CMakeLists.txt
   :language: cmake
   :lines: 36-38

Just like before, this creates a CMake library target that will get built to <build dir>/lib/libcalc_pi.a.

Next, we create an executable named example_2 and link in the previously created library target:

.. literalinclude:: tutorial/calc_pi/CMakeLists.txt
   :language: cmake
   :lines: 41-43

The DEPENDS_ON parameter properly links the previously defined library into this executable without any more work or CMake function calls.

blt_add_library

This is another core BLT macro. It creates a CMake library target and associates the given sources and headers along with handling dependencies the same way as blt_add_executable does. It also provides a few commonly used build options, such as overriding the output name of the library and the output directory. It defaults to building a static library unless you override it with SHARED or with the global CMake option BUILD_SHARED_LIBS.