mirror of
https://github.com/ttroy50/cmake-examples.git
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114 lines
3.0 KiB
Plaintext
114 lines
3.0 KiB
Plaintext
= Configure Files Generation
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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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During the call to cmake it is possible to create files that use variables from
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the CMakeLists.txt and cmake cache. During CMake generation the file is copied to a
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new location and any cmake variables are replaced.
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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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├── main.cpp
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├── path.h.in
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├── ver.h.in
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```
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* CMakeLists.txt - Contains the CMake commands you wish to run
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* main.cpp - The source file with main
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* path.h.in - File to contain a path to the build directory
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* ver.h.in - File to contain the version of the project
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# Concepts
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## Configure Files
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To do variable substitution in a file you can use the `configure_file()` function
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in CMake. This core arguments for this function are source file and destination file.
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[source,cmake]
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----
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configure_file(ver.h.in ${PROJECT_BINARY_DIR}/ver.h)
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configure_file(path.h.in ${PROJECT_BINARY_DIR}/path.h @ONLY)
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----
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The first example above, allows the variable to be defined like a CMake variables using
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the `${}` syntax or an `@@` in the ver.h.in file. After generation a new file ver.h will be available
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in the `PROJECT_BINARY_DIR`.
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```
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const char* ver = "${cf_example_VERSION}";
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```
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The second example, only allows variables to be defined using the `@@` syntax in the path.h.in file.
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After generation a new file path.h will be available in the `PROJECT_BINARY_DIR`.
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```
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const char* path = "@CMAKE_SOURCE_DIR@";
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```
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# Building the Example
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[source,bash]
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----
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$ 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/03-code-generation/configure-files/build
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$ ls
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CMakeCache.txt CMakeFiles cmake_install.cmake Makefile path.h ver.h
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$ cat path.h
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#ifndef __PATH_H__
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#define __PATH_H__
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// version variable that will be substituted by cmake
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// This shows an example using the @ variable type
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const char* path = "/home/matrim/workspace/cmake-examples/03-code-generation/configure-files";
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#endif
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$ cat ver.h
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#ifndef __VER_H__
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#define __VER_H__
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// version variable that will be substituted by cmake
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// This shows an example using the $ variable type
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const char* ver = "0.2.1";
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#endif
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$ make
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Scanning dependencies of target cf_example
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[100%] Building CXX object CMakeFiles/cf_example.dir/main.cpp.o
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Linking CXX executable cf_example
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[100%] Built target cf_example
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$ ./cf_example
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Hello Version 0.2.1!
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Path is /home/matrim/workspace/cmake-examples/03-code-generation/configure-files
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----
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