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help #include

a.h:
struct A {
   int a;
};

b.h:
struct B {
   struct A ba;
};

c.c:
#include "a.h"
#include "b.h"

</prev>

compiler complains struct A in file b.h is undefined.  I would think that by include a.h before b.h in c.c, it would see the struct A definition?

I know I could make it compile by adding:
struct A; in b.h but just want to know why it doesn't work the way above.

Thanks,

Anh

Parents

0 Andy Neil over 20 years ago in reply to HansBernhard Broeker
"A header using data types defined in another one has to include that other header"

But in the example he posted, Anh had included both the headers:
c.c: #include "a.h" #include "b.h"
So, although what you say may be good practice in general, the code as posted should've been OK?

"unless you tried to compile b.h on its own --- e.g. by adding it to your uVision project as a source file to be compiled -- which you really shouldn't do."

Quite so.
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0 Andy Neil over 20 years ago in reply to HansBernhard Broeker
"A header using data types defined in another one has to include that other header"

But in the example he posted, Anh had included both the headers:
c.c: #include "a.h" #include "b.h"
So, although what you say may be good practice in general, the code as posted should've been OK?

"unless you tried to compile b.h on its own --- e.g. by adding it to your uVision project as a source file to be compiled -- which you really shouldn't do."

Quite so.
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0 Andy Neil over 20 years ago in reply to Andy Neil
Well, I just tried
#include <stdio.h> #include "a.h" #include "b.h" void main( void ) { printf( "Hello, world!\n" ); }
and it compiled without error!
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0 HansBernhard Broeker over 20 years ago in reply to Andy Neil
But in the example he posted, Anh had included both the headers:

... in the .c file. That's not solving the problem, it's just avoiding the symptoms. File b.h, as-is, is incomplete. You can't just put

#include "b.h"
in any given C source file --- you have to remember to

#include "a.h"
first. That's a deficiency of b.h. It may not seem too bad in this simple case, but it'll bite back as soon as you try that same tactics in larger projects.
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0 Anh Phan over 20 years ago in reply to HansBernhard Broeker

Thanks guys,

I think I forgot to save the changes to "a.h". It works now.... "a.h" contains a lot of things including one struct needed for "b.h". I am more inclined to include headers from other development groups in .c rather than .h (person reasons).

Anh
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