General function prototype and header files question

[towed]

Say you declare in your header a function prototype and an argument of it is a structure that is in another header file. Do you have to have that type definition of that structure in this header file where the function prototype is located or does it not matter?

[itCbitC]

Say you declare in your header a function prototype and an argument of it is a structure that is in another header file. Do you have to have that type definition of that structure in this header file where the function prototype is located or does it not matter?

Yep! you need the header file that typedefs the struct otherwise the compiler will barf.

[laserlight]

Say you declare in your header a function prototype and an argument of it is a structure that is in another header file. Do you have to have that type definition of that structure in this header file where the function prototype is located or does it not matter?

No, you do not need the definition of that structure in that header file. However, you do need a declaration of that structure in that header file, before the declaration of that function, and then you need the definition of that structure in the source file that defines that function.

[grumpy]

No, you do not need the definition of that structure in that header file. However, you do need a declaration of that structure in that header file, before the declaration of that function, and then you need the definition of that structure in the source file that defines that function.

..... if that function accesses any member of any instance of that structure.

[Bayint Naung]

Do you have to have that type definition of that structure in this header file where the function prototype is located or does it not matter?

You don't need to have. Here is an example.

[towed]

I don't know. I had a problem with my code compiling and after switching the function prototype to the other header file (where the type definition is), it finally compiles. Which would suggest it has to...?

[MK27]

I don't know. I had a problem with my code compiling and after switching the function prototype to the other header file (where the type definition is), it finally compiles. Which would suggest it has to...?

That is the easiest and most obvious way. If you have a header file that you include with function prototypes that contain references to a so far undefined datatype, of course there is an issue. If the header file with prototypes is read in before the actual structure is defined, you can include a structure "prototype" (ie, declaration) with the function prototypes. Eg:

struct something {
  [blah blah]
};

is the definition.

struct something;

is a declaration with no definition. Since function prototypes do not contain references to struct members, etc, the struct does not have to be defined, it only has to be declared for them to pass the compiler.

Obviously, the struct does have to be fully defined before the functions are, but that could be in a subsequently included file or in a pre-compiled linked object.