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Two enum definitions of the same variable

I've noticed some code in the linux kernel with the following:

In the file s3c-dma-pl330.h there is a definition:

enum dma_ch {
...
};

and at the end of that file there is: #include <plat/dma.h> In that file (dma.h) there is: enum dma_ch; No extern is written, can you tell what is actually happens?

Does dma_ch in dma.h is the same as in s3c-dma-pl330.h? Why isn't there the extern specifier?

Solution

  • enum dma_ch; is a forward declaration of the enumeration.

    We use extern when we want to refer to an instance of an object that is found in (possibly) some other translation unit. dma_ch is not an object, it is a type.