why do we use function definition in header file and function declaration in obj
why can,t both be at header file?
policeachan 0 Newbie Poster
Dave Sinkula 2,398 long time no c Team Colleague
This is because when you have several modules, you don't want the code to be in more than one place.
The #include directive essentially copies the contents of the file into your source module. If you have 5 modules that each include a header that contains actual code, you will have 5 individual copies of that same code. That might work fine for compiling each module, but the linker will complain about which of the 5 you may have meant.
The function declaration (prototype) can exist in the header, be included by many modules, and only tells the compiler the function "signature" -- whether or not it is being used correctly in each module. The function definition can only exist once.
[Note that you have definition and declaration backwards.]
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