[C] Trouble with pointers to unions in structs and floats and oh god.

[Dr Magnusson]

For some reason, my compiler doesn't agree with my union-in-structure format.

Here's the code:
[cpp]
// My structures

typedef struct _Variable JazzVariable;
typedef union _Value JazzValue;

union _Value {
char *Char;
float Float;
};

struct _Variable {
char *Name;
JazzValue *Value;
};

[/cpp][cpp]
// Elsewhere..

void Jazz_SetNumber( JazzVariable* Variable, float Number ) {
Variable->Value.Float = Number; // This is line 40
}
[/cpp]

And here's the error I'm getting:

jazz.c|40|error: request for member `Float' in something not a structure or union|

I have absolutely no idea why it disagrees with me on this, I've read through tons of pages, documentation of operators and as far as I can tell, I'm doing it right (. for members, -> for pointers), but it simply won't work!

The (dot) operator doesn't like me at all. This problem also happened when I changed another member of the Variable struct to regular member instead of a pointer to one. It still wouldn't accept the dot operator.

If I use -> instead of . (regardless of whether Float is a pointer or member) it crashes with a segmentation fault.

Any ideas?

I'm not sure what kind of information you'd need, so please do ask if I left something vital out. Also, I should note that I have removed some of the stuff from the script that isn't related to this problem.

[jA_cOp]

You can't use the dot on a pointer. The reason -> causes a segmentation fault is because you didn't initialize the pointer. Simple as that.

[Dr Magnusson]

Oh, now I get it, the -> is of course for the struct not the member.

Thank you so much, now I can get on with completely useless and less awesome version of Lua.

[jA_cOp]

[QUOTE=Dr Magnusson;16985577]Oh, now I get it, the -> is of course for the struct not the member.[/QUOTE]

No, it is for the member, and that member is a pointer, so you need to use the dereference operator (->) to use it.

You probably want it like this:
[cpp]
typedef struct {
char *Name;
union
{
char* Char;
float Float;
} Value;
} JazzVariable;

void Jazz_SetNumber( JazzVariable* Variable, float Number )
{
Variable->Value.Float = Number;
}
[/cpp]

[Dr Magnusson]

But the float is not a pointer?

[jA_cOp]

[QUOTE=Dr Magnusson;16985777]But the float is not a pointer?[/QUOTE]

And you're not dereferencing the float anywhere, either :)

[Dr Magnusson]

Then why do I get a compiler error since I'm not dereferencing a non-pointer member?

[jA_cOp]

[QUOTE=Dr Magnusson;16985811]Then why do I get a compiler error since I'm not dereferencing a non-pointer member?[/QUOTE]

Because, in your code, you need to dereference both the Variable pointer and the Value pointer:
[cpp]
Variable->Value->Float = Number;
[/cpp]

[Cathbadh]

The line needs to be

Variable->Value->Float = number;

Value is a [I]pointer[/I] to a union. You dereference it and access the member with the second ->

[editline]03:08PM[/editline]

In any case,

Object->member

is just shorthand for

(*Object).member

[Dr Magnusson]

Am I correct in using malloc when initializing my JazzVariables?

[cpp]
JazzInstance *Instance = malloc( sizeof( JazzInstance ) );
// Start setting stuff here
[/cpp]

I'm asking, cause whenever I attempt to check the ->Type of the variable, I get a segmentation fault again.

Structures
[cpp]
typedef struct _Variable JazzVariable;

typedef enum _Type {
TYPE_NULL = 0,
TYPE_NUMBER = 1,
TYPE_STRING = 2,
TYPE_CFUNCTION = 3
} JazzType;

struct _Variable {
char *Name;
JazzType Type;
JazzValue Value;
JazzVariable *Table;
};
[/cpp]

This causes the fault
[cpp]
int Jazz_IsString( JazzVariable *Variable ) {
return Variable->Type == TYPE_STRING;
}
[/cpp]

And finally where I got the variable from
[cpp]
JazzVariable *Jazz_NewString( char *String ) {
JazzVariable *Variable = malloc( sizeof( JazzVariable ) );
Jazz_SetString( Variable, String );

return Variable;
}
[/cpp]

[B]Edit:[/B]

You know what, this very likely has nothing to do with this code at all, seeing as I'm not getting unless under some special circumstances.. Gonna look into this.

[jA_cOp]

Post the code involved.

[Dr Magnusson]

Problem was that I had to tell my host application to rebuild itself, or else the updated version of the library of course wouldn't get compiled into it :)