Question

I’d like to include in na single static C program a bunch of data (say, images, but also other data, embedded in executable since I’m working on an embedded platform without files).

Thus, I wrote a little img2c creating const data from my data files, creating a file with static const arrays initializers to be put to flash (using C99 nice features)

My question is, should I put them in a .h file, like I’ve seen many times – by example gimp can save as .h files, not .c files – or in a .c file, referenced in a header with just the const extern declaration for further references, without having to include all data and pass it all to the compiler, and redeclare it each time I use it ?

Preprocessor macros are out of the question, since I’ll reference their address, not include the whole data each time.

Answer 1

Header files in C are nothing special; the .h extension won’t change how the compiler handles them. It’s more of a hint for humans “this file probably doesn’t contain any code”.

So if you put actual binary data in there, the compiler will create a copy of the array in each file in which you include the header (instead of simply adding a reference to a shared global array).

GIMP creates a header file because it doesn’t know how you plan to use the data. The idea is that you’ll include this header file exactly once in a .c file which then processes the data in some way. If it wrote a .c file and you made changes to the code, GIMP would have to merge the changes when you ask it to update the data – it would be messy.