How to nest global structure variables?

[alchemista]

Hello, I'm trying to declare some global variables that are structures. However, some of them have nested structures and the compiler complains that the initializer is not a constant type. I thought this may be because the compiler may pad a structure, however it should be able to know this when compiling. Also, I tried using the -fpack-struct option of gcc and still I get the same error. Here's a sample of what I'm trying to do:

typedef struct {
float a;
float b;
} struct1_t;

static struct1_t NULL_STRUCT = {0.0, 0.0};

typedef struct {
float a;
struct1_t b;
} struct2_t;

static struct2_t NULL_STRUCT2 = {0.0, NULL_STRUCT};

However, this will not work. I get initializer not constant on trying to initialize the NULL_STRUCT2. How can I do such a thing in C? I'm using the gcc compiler btw.

Thanks!

 

[ami123]

One work-around will be to replace the line
static struct1_t NULL_STRUCT = {0.0, 0.0};
with
#define NULL_STRUCT {0.0, 0.0 }

cheers
amit
crazy_indian@lycos.com

to bug is human to debug devine

 

[alchemista]

I did think about that except for that if I then want to do some normal assignments, I don't think it'd work?

For example...

struct1_t a;

a = NULL_STRUCT;

or would that always work?

Thanks for the reply.

 

[ami123]

a = NULL_STRUCT;
will always work as it will be handled by
the main C compiler

static struct2_t NULL_STRUCT2 = {0.0, NULL_STRUCT};
wont work as it is expanded by the preprocessor.

cheers
amit
crazy_indian@lycos.com

to bug is human to debug devine

 

[dchoulette]

The NULL_STRUCT defined this way:

static struct1_t NULL_STRUCT = {0.0, 0.0};

is NOT a constant, it is a variable (so your compiler complains).

I would use:

#define NULL_STRUCT_INIT {0.0, 0.0}
const static struct1_t NULL_STRUCT = NULL_STRUCT_INIT;

This way you can use NULL_STRUCT_INIT to initialize static variable and the NULL_STRUCT variable to use for affectations other than initializations.