How replace string in a file with value of current directory using CMake

Question

I'm trying to make another guy's research code reproducible, so that others don't have the same trouble I'm having right now. But, I'm lacking the experience with cmake for that. Here is what I could do after reading the docs:
In the same folder as my CMakeLists.txt I have a file called io_utils.h with a ROOT_PATH variable whose value is VALUE_ROOT_PATH. I want to replace that string with the value of the file's current directory. So I tried to add the following to CMakeLists.txt:

# Set ROOT_PATH in io_utils.h
FIND_PATH(BUILD_PATH CMakeLists.txt . )
FILE(READ ${BUILD_PATH}io_utils.h IO_UTILS)
STRING(REGEX REPLACE "VALUE_ROOT_PATH" "${BUILD_PATH}" MOD_IO_UTILS "${IO_UTILS}" )
FILE(WRITE ${BUILD_PATH}io_utils.h "${MOD_IO_UTILS}")

I tried to make and install that but it is not working, the file isn't changed. What's wrong with what I did?

Answer 1

I suggest a different approach using the configure_file cmake macro. First, you create a template file that references any variables you plan to set in cmake, then the macro substitutes the actual value in place of the variable. For example, let's say we have a template file io_utils.h.in that looks something like this:

const char* ROOT_PATH = "${BUILD_PATH}";

In your CMakeLists.txt, you can do something like this:

configure_file( io_utils.h.in io_utils.h )

When you run cmake, it will use the first file as a template (io_utils.h.in here) to generate the second file (called io_utils.h here) with the value substituted in:

const char* ROOT_PATH = "/path/to/CMakeLists.txt";

By the way, CMake has a built-in variable that references the directory with the top-level CMakeLists.txt called CMAKE_SOURCE_DIR. Try replacing BUILD_PATH above with this variable.