Why can't I find many structs definition in header files of PDFL SDK?

Forum|Forum|4 years ago
December 7, 2021
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When I follow the header files in PDFL SDK, I found there are many structs which don't have a complete type.

For example, there is a definition:

typedef struct _t_PDDoc *PDDoc;

However, there is no definition of `struct _t_PDDoc`. And I also don't find any code which make it import.

So, how can the code complie successfully? What is the type indeed? When I try to use the `struct _t_PDDoc` directly in my code, there is always a mistake made by VS.

Windows

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The code can compile successfully because that is how C and C++ are defined. Pointers to an undefined structure are all pointers so they can be compiled. The compiler does type checking so they are distinct.

These are called opaque types. There are many in the PDF library (in this case, identical to the Acrobat SDK). I have no idea why you would want to use the PDDoc structure in your code, but whatever the reason, you can't.

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The code can compile successfully because that is how C and C++ are defined. Pointers to an undefined structure are all pointers so they can be compiled. The compiler does type checking so they are distinct.

These are called opaque types. There are many in the PDF library (in this case, identical to the Acrobat SDK). I have no idea why you would want to use the PDDoc structure in your code, but whatever the reason, you can't.