“Configured” Header Files¶

Problem ¶

Want to output project version in executables
⟶ Set version using PROJECT()

Output using MESSAGE()

PROJECT(Demo VERSION 42.666)
MESSAGE(DEBUG "Major: ${Demo_VERSION_MAJOR}")
MESSAGE(DEBUG "Major: ${Demo_VERSION_MINOR}")

Question: how to make those available to compiled code?
Answer: CONFIGURE_FILE()

Configured Files ¶

Header file template that contains CMake variable substitutions

10-configure-file/DemoConfig.h.in¶

// This file is generated, do not modify

#define DEMO_MAJOR @Demo_VERSION_MAJOR@
#define DEMO_MINOR @Demo_VERSION_MINOR@

Let CMake perform substitutions

CONFIGURE_FILE(DemoConfig.h.in DemoConfig.h)

Converted to ${CMAKE_CURRENT_BINARY_DIR}/DemoConfig.h

Use In Compiled Code ¶

Pick up CMake variables from configure file (10-configure-file/bin/hello-first.cpp and 10-configure-file/bin/hello-second.cpp)
```
#include <DemoConfig.h>
// ...
std::cout << "Version " << DEMO_MAJOR << '.' << DEMO_MINOR << std::endl;
```

Does not compile ⟶ include path missing

bin/hello-first.cpp:4:10: fatal error: DemoConfig.h: No such file or directory
    4 | #include <DemoConfig.h>
      |          ^~~~~~~~~~~~~~

Solution: set include path for all (to add a dependency would be overkill but could be done)
Toplevel CMakeLists.txt¶
```
INCLUDE_DIRECTORIES(${CMAKE_CURRENT_BINARY_DIR})
```