pointer to stuct data

[Robert S]

hello,
I am investigating a code,which has data struct deelacration as follow:

typedef struct {
char *infile;
char inoptsbuf[10];
char *outfile;
} cmdoption_a;

cmdoption_a *cmdoption;

and intialization as follow:

cmdoption->infile=1;
cmdoption->outfile=1;
cmdoption->inoptsbuf='\0' ;

I am really confused since an integer is assign to the above variables?!!!!
any help??!!

bob

[Artie Gold]

Robert S wrote:

hello,
I am investigating a code,which has data struct deelacration as follow:

typedef struct {
char *infile;
char inoptsbuf[10];
char *outfile;
} cmdoption_a;

cmdoption_a *cmdoption;

and intialization as follow:

cmdoption->infile=1;
cmdoption->outfile=1;
cmdoption->inoptsbuf='\0' ;

I am really confused since an integer is assign to the above variables?!!!!
any help??!!

You *should* be confused; the code (as you've quoted it) makes no sense
at all, would (should?) not compile and certainly couldn't possibly work.

Why not post the *real* code (i.e. cut and paste, don't transcribe)? I'm
sure someone here could clear up any confusion.

HTH,
--ag

--
Artie Gold -- Austin, Texas
http://it-matters.blogspot.com (new post 12/5)
http://www.cafepress.com/goldsays

[Robert S]

thanks
It is a transcoder proram which compile and run without a problem
here is the code:

typedef struct {

char *infile;
/* The input image file. */

int infmt;
/* The input image file format. */

char *inopts;
char inoptsbuf[OPTSMAX + 1];

char *outfile;
/* The output image file. */

int outfmt;

char *outopts;
char outoptsbuf[OPTSMAX + 1];

int verbose;
/* Verbose mode. */

int debug;

int version;

int_fast32_t cmptno;

int srgb;

} cmdopts_t;
..
..
..
..
..
cmdopts_t *cmdopts;

cmdopts->infile = 0;
cmdopts->infmt = -1;
cmdopts->inopts = 0;
cmdopts->inoptsbuf[0] = '\0';
cmdopts->outfile = 0;
cmdopts->outfmt = -1;
cmdopts->outopts = 0;
cmdopts->outoptsbuf[0] = '\0';
cmdopts->verbose = 0;
cmdopts->version = 0;
cmdopts->cmptno = -1;
cmdopts->debug = 0;
cmdopts->srgb = 0;
..
..
..
..

"Artie Gold" <ar*******@aust in.rr.com> wrote in message news:3c******** *****@individua l.net...

Robert S wrote:

hello,
I am investigating a code,which has data struct deelacration as follow:

typedef struct {
char *infile;
char inoptsbuf[10];
char *outfile;
} cmdoption_a;

cmdoption_a *cmdoption;

and intialization as follow:

cmdoption->infile=1;
cmdoption->outfile=1;
cmdoption->inoptsbuf='\0' ;

I am really confused since an integer is assign to the above variables?!!!!
any help??!!

You *should* be confused; the code (as you've quoted it) makes no sense
at all, would (should?) not compile and certainly couldn't possibly work.

Why not post the *real* code (i.e. cut and paste, don't transcribe)? I'm
sure someone here could clear up any confusion.

HTH,
--ag

--
Artie Gold -- Austin, Texas
http://it-matters.blogspot.com (new post 12/5)
http://www.cafepress.com/goldsays

[Keith Thompson]

Please don't top-post. Your response belongs below, or interspersed
with, any quoted text.

In your original message, you wrote:

typedef struct {
char *infile;
char inoptsbuf[10];
char *outfile;
} cmdoption_a;

cmdoption_a *cmdoption;

and intialization as follow:

cmdoption->infile=1;
cmdoption->outfile=1;
cmdoption->inoptsbuf='\0' ;

but the actual code says (trimmed a bit):
typedef struct {
char *infile; [...] char *outfile; [...] char outoptsbuf[OPTSMAX + 1]; [...] } cmdopts_t; [...] cmdopts_t *cmdopts;

cmdopts->infile = 0; [...] cmdopts->outfile = 0; [...] cmdopts->outoptsbuf[0] = '\0';

Initializing a pointer with 1 almost certainly makes no sense, but 0
is a null pointer constant. I'd prefer to use the macro NULL (defined
in <stddef.h> and several other standard headers), but an unadorned 0
is perfectly legal.

This is why it's best to cut-and-paste the actual code you're asking
about rather than trying to paraphrase it; it's too easy to
accidentally change the very thing you're asking about.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Robert S]

Thanks
So 0 means NULL,however I thought '\0' means NULL
Now,how about -1 which assign as follows:

cmdopts->infile = 0;
cmdopts->infmt = -1;
cmdopts->inopts = 0;
cmdopts->inoptsbuf[0] = '\0';
cmdopts->outfile = 0;
cmdopts->outfmt = -1;
cmdopts->outopts = 0;
cmdopts->outoptsbuf[0] = '\0';
cmdopts->verbose = 0;
cmdopts->version = 0;
cmdopts->cmptno = -1;
cmdopts->debug = 0;
cmdopts->srgb = 0;
"Keith Thompson" <ks***@mib.or g> wrote in message
news:ln******** ****@nuthaus.mi b.org...

Please don't top-post. Your response belongs below, or interspersed
with, any quoted text.

In your original message, you wrote:

typedef struct {
char *infile;
char inoptsbuf[10];
char *outfile;
} cmdoption_a;

cmdoption_a *cmdoption;

and intialization as follow:

cmdoption->infile=1;
cmdoption->outfile=1;
cmdoption->inoptsbuf='\0' ;

but the actual code says (trimmed a bit):

typedef struct {
char *infile;

[...]

char *outfile;

[...]

char outoptsbuf[OPTSMAX + 1];

[...]

} cmdopts_t;

[...]

cmdopts_t *cmdopts;

cmdopts->infile = 0;

[...]

cmdopts->outfile = 0;

[...]

cmdopts->outoptsbuf[0] = '\0';

Initializing a pointer with 1 almost certainly makes no sense, but 0
is a null pointer constant. I'd prefer to use the macro NULL (defined
in <stddef.h> and several other standard headers), but an unadorned 0
is perfectly legal.

This is why it's best to cut-and-paste the actual code you're asking
about rather than trying to paraphrase it; it's too easy to
accidentally change the very thing you're asking about.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org
<http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*>
<http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Jason]

Robert S wrote:

Thanks
So 0 means NULL,however I thought '\0' means NULL
Now,how about -1 which assign as follows:

'\0' in a char sense means ascii zero. 0 in a char* sense means memory
address 0x0, or NULL.

[Keith Thompson]

"Robert S" <b_******@yahoo .com> writes:

Thanks
So 0 means NULL,however I thought '\0' means NULL
Now,how about -1 which assign as follows:

[snip]

Again, please don't top-post. And please don't send me copies of
Usenet articles by e-mail.

-1 is just the integer value -1. I believe all the members to which
-1 is assigned are integers. What -1 means is up to the application.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Keith Thompson]

"Jason" <ma******@hotma il.com> writes:

Robert S wrote:

Thanks
So 0 means NULL,however I thought '\0' means NULL
Now,how about -1 which assign as follows:

'\0' in a char sense means ascii zero. 0 in a char* sense means memory
address 0x0, or NULL.

ASCII is just one possible character representation. '\0' is a
character constant with value 0 (a null character). It happens to be
of type int, but it's used for clarity in a character context.

A null pointer is not necessarily address 0x0 (i.e., it's not
necessarily represented as all-bits-zero).

Please read section 5 of the C FAQ,
<http://www.eskimo.com/~scs/C-faq/top.html>.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Jason]

Keith Thompson wrote:

"Jason" <ma******@hotma il.com> writes:

'\0' in a char sense means ascii zero. 0 in a char* sense means memory address 0x0, or NULL.
ASCII is just one possible character representation. '\0' is a
character constant with value 0 (a null character). It happens to be
of type int, but it's used for clarity in a character context.

Of course, I forgot about other charsets.
A null pointer is not necessarily address 0x0 (i.e., it's not
necessarily represented as all-bits-zero).
I had no idea...
Please read section 5 of the C FAQ,
<http://www.eskimo.com/~scs/C-faq/top.html>.

According to section 5.5 of the FAQ, "it is the compiler's
responsibility to generate whatever bit pattern the machine uses for
that null pointer."

Thanks for setting me straight.

-Jason

[CBFalconer]

Robert S wrote:

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--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson