OpenEuphoria

1. Wrapping from C Struct

• Posted by Lone_EverGreen_Ranger Sep 11, 2013
• 1601 views

Hello,

How do you wrap the data of a struct from a C source file? Such as this

typedef struct    {      
unsigned int width;       
unsigned int height;      
unsigned int bitsPerPixel;     
} sfVideoMode; 

Is there a way to do this?

public constant xsfVideoMode = define_c_func(sf_gfx,"sfVideoMode",{C_UINT,C_UINT,C_UINT},C_POINTER) 
 
public function sfVideoMode(atom w,atom h,atom bits) 
	 
	return c_func(xsfVideoMode,{w,h,bits}) 
 
end function 

3. Re: Wrapping from C Struct

• Posted by Lone_EverGreen_Ranger Sep 12, 2013
• 1506 views

include std/machine.e 
 
memstruct struct_sfVideoMode 
   unsigned int width 
   unsigned int height 
   unsigned int bitsPerPixel 
end memstruct 
 
--// allocate 
atom sfv = allocate(sizeof(struct_sfVideoMode)) 
sfv.struct_sfVideoMode = {0} 
 
--// fill (call your function) 
--// i assume your function returns a pointer to 
--// the appropriate struct 
sfv = sfVideoMode(w, h, bits) 
 
--// access struct members 
? sfv.struct_sfVideoMode.width 
? sfv.struct_sfVideoMode.height 
? sfv.struct_sfVideoMode.bitsPerPixel 
 
--// cleanup 
free(sfv) 

Thanks, however Eu 4.1 isn't out yet. Though I could use the bleeding edge version. Any news on when 4.1 will be released?

5. Re: Wrapping from C Struct

• Posted by mattlewis (admin) Sep 12, 2013
• 1466 views

typedef struct    {      
unsigned int width;       
unsigned int height;      
unsigned int bitsPerPixel;     
} sfVideoMode; 

A C struct defines the way C code lays out data in memory. Basically, you have to peek and poke using offsets. So...

constant 
    SFVM_WIDTH        = 0, 
    SFVM_HEIGHT       = 4, 
    SFVM_BITSPERPIXEL = 8, 
    SFVM_SIZEOF       = 12 
 
atom sfvm = allocate( SFVM_SIZEOF ) 
poke4( sfvm + SFVM_WIDTH,  100 ) 
poke4( sfvm + SFVM_HEIGHT, 200 ) 
poke4( sfvm + SFVM_BITSPERPIXEL, 8 ) 
 
? peek4u( sfvm + SFVM_BITSPERPIXEL ) -- get the bits per pixel 
 
-- ...etc... 

You can, of course, wrap those as functions / procedures for convenience.

Matt

7. Re: Wrapping from C Struct

• Posted by petelomax Sep 13, 2013
• 1436 views

typedef struct    {      
unsigned int width;       
unsigned int height;      
unsigned int bitsPerPixel;     
} sfVideoMode; 

public constant xsfVideoMode = define_c_func(sf_gfx,"sfVideoMode",{C_UINT,C_UINT,C_UINT},C_POINTER) 
 
public function sfVideoMode(atom w,atom h,atom bits) 
	 
	return c_func(xsfVideoMode,{w,h,bits}) 
 
end function 

I see somewhat of a complete misunderstanding here: a typedef is not entirely dissimilar to a Euphoria type, in that just as:

constant DHOUR=1, DMIN=2, DSEC=3 
[global] type DATE(object t) 
    if sequence(t) and length(t)=3  
    and integer(t[DHOUR]) and t[DHOUR]>=0 and t[DHOUR]<=23  
    and integer(t[DMIN]) and t[DMIN]>=0 and t[DMIN]<=59  
    and integer(t[DSEC]) and t[DSEC]>=0 and t[DSEC]<=59 then 
        return TRUE 
    end if 
    return FALSE 
end type 

(sorry that turned out a bit more verbose than planned when I started typing) does not define anywhere to store eg 2:29:26am, for which you need say:

DATE mydate 

then neither does that "typedef sfVideoMode" define any data (that you might better be able to locate using define_c_var), nor (unlike Eu types) does it define a function.

Not that I am faulting what others have said in this thread. In C and C++ you need to digest the headers, macros, typedefs, etc before getting to the code that matters, and I just felt I should point out that a typedef struct is actually neither code nor data, and "sfVideoMode" is almost guaranteed to be the wrong identifier to use.

Pete