Indenting #defines

cc-preprocessorcode formattingindentation

I know that #defines, etc. are normally never indented. Why?

I'm working in some code at the moment which has a horrible mixture of #defines, #ifdefs, #elses, #endifs, etc. All these often mixed in with normal C code. The non-indenting of the #defines makes them hard to read. And the mixture of indented code with non-indented #defines is a nightmare.

Why are #defines typically not indented? Is there a reason one wouldn't indent (e.g. like this code below)?

#ifdef SDCC
    #if DEBUGGING == 1
        #if defined (pic18f2480)
            #define FLASH_MEMORY_END 0x3DC0
        #elif defined (pic18f2580)
            #define FLASH_MEMORY_END 0x7DC0
        #else
            #error "Can't set  up flash memory end!"
        #endif
    #else
        #if defined (pic18f2480)
            #define FLASH_MEMORY_END 0x4000
        #elif defined (pic18f2580)
            #define FLASH_MEMORY_END 0x8000
        #else
            #error "Can't set  up flash memory end!"
        #endif
    #endif
#else
    #if DEBUGGING == 1
        #define FLASH_MEMORY_END 0x7DC0
    #else
        #define FLASH_MEMORY_END 0x8000
    #endif
#endif

Best Answer

Pre-ANSI C preprocessor did not allow for space between the start of a line and the "#" character; the leading "#" had to always be placed in the first column.

Pre-ANSI C compilers are non-existent these days. Use which ever style (space before "#" or space between "#" and the identifier) you prefer.

http://www.delorie.com/gnu/docs/gcc/cpp_48.html

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