Passing pointer array to function

[Tatu Portin]

I have a struct:

typedef struct {
char **user_comments ;
int *comment_wds;
int comments;
char *vendor;
} vorbis_comment;
void func (char **table)
{
return;
}

int main (void)
{
vorbis_comment vc;
/* This part GCC doesn't like */

func (vc.user_commen ts);

return 0;
}

GCC (3.1) would say that

warning: passing arg 1 of 'func' from incompatible pointer type

But still my code in 'func' (not posted, above is an example) works correctly,
utilizing whole '**table'.

Now what I want to ask is that which is the legal way to make a call of this
kind? Or is it just a bug or "feature" of GCC?
I am compiling with a commandline:

gcc -Wall -pedantic -ansi -mcpu=athlon -ffast-math -O2

[Tatu Portin]

Tatu Portin wrote:

Ok. First post was wrong. (I thought that simplifying would do the same.
It didn't.)

Here we are:
42:int fprint_comments _formatted
43: ( FILE *tg
44: , const vorbis_comment *vc)
45:{
46: register int i;

....

69: if (flag) {

70: entry = has_str (s_album, vc->user_comment s, vc->comments);

71: val = strpbrk (vc->user_comment s[entry], "=");
72: val++;
73: fprintf (tg, "%s\n", val);
74:
75: flag = 0;
76: }

....

90: return 0;
91:}

gcc -Wall -pedantic -ansi -mcpu=athlon -ffast-math -O2 cdmaker.c
cdmaker_1.o -o cdmaker.exe
cdmaker.c In function 'fprint_comment s_formatted':
cdmaker.c:70 warning: passing arg 2 of 'has_str' from incompatible
pointer type
Function prototypes:
int fprint_comments _formatted
( FILE *tg
, const vorbis_comment *vc);

int has_str
( const char *str
, const char **table
, int ent); /* Number of entries in '**table' */
Struct definition:
typedef struct {
char **user_comments ;
int *comment_wds;
int comments;
char *vendor;
} vorbis_comment;

Thank you all. The problem was, as you said, the const qualifier.

But is anyone capable of saying why exactly this fails? (with 'const char **table')

[Andrey Tarasevich]

Tatu Portin wrote:

...
But is anyone capable of saying why exactly this fails? (with 'const char **table')
...

The reason why type 'T**' is not implicitly convertible to type 'const
T**' (in both C and C++) is explained well in the C++ FAQ

http://www.parashift.com/c++-faq-lit...html#faq-18.15

This is C++ FAQ, but the reasoning applies immediately to C as well. In
short, this conversion, if it was allowed, would create a large hole in
the "wall" of const-correctness checks :) Sometimes it might appear to
be illogical though.

It might be worth noting that C++ allows implicit 'T**' -> 'const T*
const*' conversion. C doesn't.

--
Best regards,
Andrey Tarasevich