Hi Guys,
I was going through gdbm-1.8.3 source (http://ftp.gnu.org/gnu/gdbm/
gdbm-1.8.3.tar.gz) and found this strange thing : all the exposed
functions of gdbm work with GDBM_FILE pointer (which is returned by
gdbm_open), but in the implementation of gdbm functions (e.g.
gdbm_open in gdbmopen.c)work with a structure called gdbm_file_info.
Now GDBM_FILE is defined like this in gdbm.h an exposed header :
typedef struct { int dummy[10];} *GDBM_FILE;
but gdbm_file_info is a structure which is a lot bigger than this.
For e.g. in gdbm.h gdbm_open is defined as :
extern int gdbm_store __P((GDBM_FILE, datum, datum, int)); /* __P(x)
is x if it is standard C or C++ else _P(x) is () */
but in its definition it is like this :
int
gdbm_store (dbf, key, content, flags)
gdbm_file_info *dbf;
datum key;
datum content;
int flags;
I have these questions : (I searched previous archives of c.l.c, but
only found mention of typedef struct {int dummy[10];} *GDBM_FILE; in a
post called "What makes C _not_ a subset of C++, where it said that
this particular declaration is illegal in C++)
1. How does this sort of code compiles in standard C ? ( What function
prototype matching rule of C applies here ?) When I checked in the
generated Makefile there wasn't any special flags that were passed to
gcc.
2. Why was this done ? My first guess is because the author did not
want to expose the gdbm_file_info structure in gdbm.h so that he can
change it between different releases preserving compatibility (?) Also
to keep the external interface clean.
3. Is this safe ? Will it work in all the compilers and machines i.e.
is it ****table ?
Any help is appreciated.
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