Initializing an Array of Pointers to Structs

[ccdrbrg]

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]

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.

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],
};

 

[ccdrbrg]

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

Chad

 

[Eric Sosman]

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

(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.

 

[Chris Torek]

(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.

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."