compile a cpp file with multiple different header files

Question

I have a single cpp file and multiple hpp files. For each hpp file, I want to create an executable using the same cpp file. The header files have different names. Can I do this in CMake?

So I have

source_1.cpp

header_1.hpp header_2.hpp ...

and I want to create

executable_1 executable_2 ...

You could use a cascade of macros #ifdef exe1 and pass different macros as preprocessor options, e.g. for GCC it's -D. For -Dexe1 the first header is included and for -Dexe2 the second header is included. — Thomas Sablik
– Thomas Sablik, Commented Mar 15, 2021 at 12:13
Should there be any difference between the different executables? — eerorika
– eerorika, Commented Mar 15, 2021 at 12:14
I have 40 different header files and I want to automate it. Each header file is a submission from different people. I am grading their homework — ultrafrog
– ultrafrog, Commented Mar 15, 2021 at 12:16
Why are they "header" files? Why not have them submit the file with cpp suffix? That way you can just compile it. — eerorika
– eerorika, Commented Mar 15, 2021 at 12:19

Some programmer dude · Accepted Answer · 2021-03-15 12:18:14Z

The C++ preprocessor can use macros for #include.

That is, you can have something like:

#include HEADER_FILE_TO_INCLUDE

Then when building the source file you could define the macro on the command-line:

g++ -DHEADER_FILE_TO_INCLUDE="\"header_1.hpp\"" source_1.cpp

To do this with CMake you first of all need multiple executable targets, where you specify the same source file for each target.

Then you can use target_compile_definitions to specify the macro and the header file to use.

Something like

add_executable(executable_1 source_1.cpp)
target_compile_definitions(executable_1 HEADER_FILE_TO_INCLUDE="header_1.hpp")

add_executable(executable_2 source_1.cpp)
target_compile_definitions(executable_2 HEADER_FILE_TO_INCLUDE="header_2.hpp")

If all header files are named header_X.hpp, with X just being a sequence number, then you could easily create a loop from 1 to the max value of header file numbers.

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