Initializing an Array of Pointers to Structs

[ccdrbrg@yahoo.com]

I am trying to initialize an arrary of
pointers to structs with constants.

Sample code:

struct mystruct {
char *text;
int number;
};

struct mystruct *array[] = {
{"string1", 1},
{"string2", 2},
{"string3", 3},
};

GCC complains: "braces around scaler initializer"

I would think {"string1", 1} would be
replaced with an address upon compilation.

For example,
char *strings[] = {"string1", "string2", NULL};
works.

Any help would be appreciated.

Chad

[Eric Sosman]

Re: Initializing an Array of Pointers to Structs



ccdrbrg@yahoo.c om wrote:[color=blue]
> I am trying to initialize an arrary of
> pointers to structs with constants.
>
> Sample code:
>
> struct mystruct {
> char *text;
> int number;
> };
>
> struct mystruct *array[] = {
> {"string1", 1},
> {"string2", 2},
> {"string3", 3},
> };
>
> GCC complains: "braces around scaler initializer"
>
> I would think {"string1", 1} would be
> replaced with an address upon compilation.
>
> For example,
> char *strings[] = {"string1", "string2", NULL};
> works.
>
> Any help would be appreciated.[/color]

struct mystruct array_data[] = {
{ "string1", 1 },
{ "string2", 2 },
{ "string3", 3 },
};

struct mystruct *array[] = {
&array_data[0], /* or `array_data + 0' */
&array_data[1],
&array_data[2],
};

--
Eric.Sosman@sun .com

[ccdrbrg@yahoo.com]

Re: Initializing an Array of Pointers to Structs

Is it possible to initialize the array without declaring
an intermediate variable to get an address?

Chad

[Eric Sosman]

Re: Initializing an Array of Pointers to Structs



ccdrbrg@yahoo.c om wrote:[color=blue]
> Is it possible to initialize the array without declaring
> an intermediate variable to get an address?[/color]

(See up-thread for snipped context: He wants to initialize
an array of pointers to structs that are also initialized.)

No. The string literal is the only C construct that
creates and initializes an "anonymous" object. All other
initialized objects must have names.

--
Eric.Sosman@sun .com

[Chris Torek]

Re: Initializing an Array of Pointers to Structs

>ccdrbrg@yahoo. com wrote:[color=blue][color=green]
>> Is it possible to initialize the array without declaring
>> an intermediate variable to get an address?[/color][/color]

In article <d3jpan$2d5$1@n ews1brm.Central .Sun.COM>
Eric Sosman <eric.sosman@su n.com> wrote:[color=blue]
> (See up-thread for snipped context: He wants to initialize
>an array of pointers to structs that are also initialized.)
>
> No. The string literal is the only C construct that
>creates and initializes an "anonymous" object. All other
>initialized objects must have names.[/color]

Except in C99, where compound literals create anonymous
objects.

For instance, in C99 (but not C89), one can write:

/* tables for decoding SCSI <code,subcode > pairs */

struct subcode {
int sc_num;
char *sc_msg;
};
struct code {
int co_num;
size_t co_nsub;
struct subcode *co_subc;
};

struct code scsi_codetab[] = {
{
0, 2,
(struct subcode [2]) {
{ 0, "0/0" },
{ 1, "0/1" },
},
},
{
1, 3,
(struct subcode [3]) {
{ 0, "1/0" },
{ 27, "1/27" },
{ 40, "1/40" },
}
},
};

(The above is not intended to be particularly useful; in particular
the code and subcode numbers are made up and the sc_msg strings are
ridiculous. But SCSI does have code/subcode pairs and the overall
technique itself is reasonable.)

Note that even though you *can* do this in C99, it is probably
better to use C89 constructs to match up the "number of subcodes"
initializer (for co_nsub) and actual table sizes automatically.
That is, writing this out "longhand" is actually less fragile:

struct subcode {
int sc_num;
char *sc_msg;
};
struct code {
int co_num;
size_t co_nsub;
struct subcode *co_subc;
};

static struct subcode sc0_table[] = {
{ 0, "0/0" },
{ 1, "0/1" },
};
static struct subcode sc1_table[] = {
{ 0, "1/0" },
{ 27, "1/27" },
{ 40, "1/40" },
};
#define COUNT_AND_TABLE (x) sizeof x / sizeof x[0], x
struct code scsi_codetab[] = {
{ 0, COUNT_AND_TABLE (sc0_table) },
{ 1, COUNT_AND_TABLE (sc1_table) },
};

There is in fact a more general rule of programming that applies
here: "if something is complex, give it a name."
--
In-Real-Life: Chris Torek, Wind River Systems
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603
email: forget about it http://web.torek.net/torek/index.html
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