CMake - Header files with preprocessor directives

Question

Is it possible to compile header files with C/C++ preprocessor direktives? (Defines)

I have a project with some header files which are without a cpp file. For example typedefs for different platforms.

I'm looking for a simple solution that can be integrated into my cmakefile.

Will they not be included in some other cpp file? If so, they are compiled there. — Bo Persson, Oct 11 '16 at 12:10
I have a lot of header files of this kind. The expense would be to great. — Erik, Oct 11 '16 at 12:18
I have misunderstood this. The header files are included in some cpp files but do not have their own cpp file. — Erik, Oct 11 '16 at 12:24
If your header files include static definitions, they are not header files. You should definitively re-design your project and move those definitions to a corresponding implementation file. If no, why compile themselves? Did you understand the idea of header files? — too honest for this site, Oct 11 '16 at 12:24
For example: #ifdef LINUX typedef int32_t t_my_int #endif | This is one part of my header file. I use this file in many projects. — Erik, Oct 11 '16 at 12:34
@Erik: Please get your favourite C++ book and read about what header files are for and how they fit into the build-process. Also recap what `#define` and `typedef` etc. actually do. You apparently have some missconceptions. — too honest for this site, Oct 11 '16 at 12:56

score 0 · Accepted Answer · answered Oct 11 '16 at 13:16

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Are you looking for precompiled headers maybe? They can be compiled by a makefile.

answered Oct 11 '16 at 13:16

UKMonkey

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I think this could be the solution. Could you show me a short example? – Erik Oct 11 '16 at 13:18

score -1 · Answer 2 · answered Oct 11 '16 at 12:23

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If your headers are included in cpp files, they will automatically be used. If they are not included, what is the point of 'compiling' them ?

So basically, the answer is no, you cannot compile only header files. The purpose of compilation is to produce an executable, a file that do actions when executed. Definitions are not actions, they do nothing on their own.

answered Oct 11 '16 at 12:23

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Actually _definitions_ are where all the action is! – too honest for this site Oct 11 '16 at 12:24
I don't get it. You mean that #define PI 3.14 is an action ? – Hexdump Oct 11 '16 at 12:34
That's a **macro** definition. The term _definition_ is well defined in C. OP apparently has not just macros, but also `typedef`s. It is not clear why he wants them to be compiled stand-along. – too honest for this site Oct 11 '16 at 12:53
OP clearly stated "defines". And i still don't get how you consider a typedef as an action. – Hexdump Oct 11 '16 at 13:03
Parenthetised words are often more an example, the might be others. And "For example typedefs for different platforms." shows there are other elements he considers. The questions is so vague, it is not clear he has no other definitions. For the terms: Read the standard! – too honest for this site Oct 11 '16 at 13:09

CMake - Header files with preprocessor directives

2 Answers2