Headers including other headers?

Headers including other headers?

[Jim Blandy]

Suppose a header file in gdb/ contains code cannot be compiled without
definitions from other header files --- it uses typedefs, structures
in a way that requires their size, etc.  Is it more proper for the
header file to #include the other headers it requires itself, or
should it be the responsibility of the .c file #including it to also
bring in its prerequisites?

In hopes that this doesn't start a really long thread of unsatisfying
disagreements: I personally think that this is not a matter of huge
consequence either way, but it's nicer to have a consistent pattern,
so having someone simply establish any reasonable guideline is more
important than the actual details of that guideline.

I'm not volunteering to convert our existing headers; I just want to
know what style is recommended for new header files.

Re: Headers including other headers?

[Andrew Cagney]

The style guide says:

http://sources.redhat.com/gdb/onlinedocs/gdbint_13.html#SEC111

> All `.c' files should include `defs.h' first.
> 
> All `.c' files should explicitly include the headers for any declarations they refer to. They should not rely on files being included indirectly.
> 
> With the exception of the global definitions supplied by `defs.h', a header file should explictily include the header declaring any typedefs et.al. it refers to.
> 
> extern declarations should never appear in .c files.
> 
> All include files should be wrapped in:
> 
>  
> 
> #ifndef INCLUDE_FILE_NAME_H
> #define INCLUDE_FILE_NAME_H
> header body
> #endif

along with:

http://sources.redhat.com/gdb/onlinedocs/gdbint_13.html#SEC107

> Declarations like `struct foo *' should be used in preference to declarations like `typedef struct foo { ... } *foo_ptr'.



(Daniel J, note clause #1 :-).

> Suppose a header file in gdb/ contains code cannot be compiled without
> definitions from other header files --- it uses typedefs, structures
> in a way that requires their size, etc.  Is it more proper for the
> header file to #include the other headers it requires itself, or
> should it be the responsibility of the .c file #including it to also
> bring in its prerequisites?
> In hopes that this doesn't start a really long thread of unsatisfying
> disagreements: I personally think that this is not a matter of huge
> consequence either way, but it's nicer to have a consistent pattern,
> so having someone simply establish any reasonable guideline is more
> important than the actual details of that guideline.
> 
> I'm not volunteering to convert our existing headers; I just want to
> know what style is recommended for new header files.

If you find you need to #include a system header file (since defs.h 
doesn't include it) then consider re-structuring the code so that GDB 
uses a host independant type - make the object opaque for instance.

Andrew