struct pointing to another struct?
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From: inhahe on 13 Aug 2010 15:54 say i have this definition: 1 typedef struct SDL_Surface { 2 Uint32 flags; /* Read-only */ 3 SDL_PixelFormat *format; /* Read-only */ 4 int w, h; /* Read-only */ 5 Uint16 pitch; /* Read-only */ 6 void *pixels; /* Read-write */ 7 SDL_Rect clip_rect; /* Read-only */ 8 int refcount; /* Read-mostly */ 9 10 /* This structure also contains private fields not shown here */ 11 } SDL_Surface; notice two pointers, format and pixels. say format has this definition. 1 typedef struct { 2 SDL_Palette *palette; 3 Uint8 BitsPerPixel; 4 Uint8 BytesPerPixel; 5 Uint8 Rloss, Gloss, Bloss, Aloss; 6 Uint8 Rshift, Gshift, Bshift, Ashift; 7 Uint32 Rmask, Gmask, Bmask, Amask; 8 Uint32 colorkey; 9 Uint8 alpha; 10 } SDL_PixelFormat; so say i want to create a mock sdl handle and pass it to some library function that requires an sdl handle. (would it even work? would i need to use an SDL_SWSURFACE?) so i make the pixelformat data using struct.pack, and make the surface data using struct.pack, but how do i link the surface data to the pixelformat data? if i just use id() it'll give me the memory address of the "box" for the string and not the string data itself. thanks.
From: Peter Otten on 13 Aug 2010 16:07 inhahe wrote: > say i have this definition: > > 1 typedef struct SDL_Surface { > 2 Uint32 flags; /* Read-only */ > 3 SDL_PixelFormat *format; /* Read-only */ > 4 int w, h; /* Read-only */ > 5 Uint16 pitch; /* Read-only */ > 6 void *pixels; /* Read-write */ > 7 SDL_Rect clip_rect; /* Read-only */ > 8 int refcount; /* Read-mostly */ > 9 > 10 /* This structure also contains private fields not shown here > */ > 11 } SDL_Surface; > > notice two pointers, format and pixels. > say format has this definition. > > > 1 typedef struct { > 2 SDL_Palette *palette; > 3 Uint8 BitsPerPixel; > 4 Uint8 BytesPerPixel; > 5 Uint8 Rloss, Gloss, Bloss, Aloss; > 6 Uint8 Rshift, Gshift, Bshift, Ashift; > 7 Uint32 Rmask, Gmask, Bmask, Amask; > 8 Uint32 colorkey; > 9 Uint8 alpha; > 10 } SDL_PixelFormat; > > so say i want to create a mock sdl handle and pass it to some library > function that requires an sdl handle. (would it even work? would i > need to use an SDL_SWSURFACE?) > > so i make the pixelformat data using struct.pack, and make the surface > data using struct.pack, but how do i link the surface data to the > pixelformat data? if i just use id() it'll give me the memory address > of the "box" for the string and not the string data itself. thanks. I think you are looking at the wrong module; you need ctypes, not struct. http://docs.python.org/library/ctypes.html Peter
From: inhahe on 13 Aug 2010 16:28 On Aug 13, 4:07 pm, Peter Otten <__pete...(a)web.de> wrote: > inhahe wrote: > > say i have this definition: > > > 1 typedef struct SDL_Surface { > > 2 Uint32 flags; /* Read-only */ > > 3 SDL_PixelFormat *format; /* Read-only */ > > 4 int w, h; /* Read-only */ > > 5 Uint16 pitch; /* Read-only */ > > 6 void *pixels; /* Read-write */ > > 7 SDL_Rect clip_rect; /* Read-only */ > > 8 int refcount; /* Read-mostly */ > > 9 > > 10 /* This structure also contains private fields not shown here > > */ > > 11 } SDL_Surface; > > > notice two pointers, format and pixels. > > say format has this definition. > > > 1 typedef struct { > > 2 SDL_Palette *palette; > > 3 Uint8 BitsPerPixel; > > 4 Uint8 BytesPerPixel; > > 5 Uint8 Rloss, Gloss, Bloss, Aloss; > > 6 Uint8 Rshift, Gshift, Bshift, Ashift; > > 7 Uint32 Rmask, Gmask, Bmask, Amask; > > 8 Uint32 colorkey; > > 9 Uint8 alpha; > > 10 } SDL_PixelFormat; > > > so say i want to create a mock sdl handle and pass it to some library > > function that requires an sdl handle. (would it even work? would i > > need to use an SDL_SWSURFACE?) > > > so i make the pixelformat data using struct.pack, and make the surface > > data using struct.pack, but how do i link the surface data to the > > pixelformat data? if i just use id() it'll give me the memory address > > of the "box" for the string and not the string data itself. thanks. > > I think you are looking at the wrong module; you need ctypes, not struct. > > http://docs.python.org/library/ctypes.html > > Peter can you (or anybody) tell me how to link one c struct to another using ctypes? Thx
From: Peter Otten on 13 Aug 2010 17:03 inhahe wrote: > On Aug 13, 4:07 pm, Peter Otten <__pete...(a)web.de> wrote: >> inhahe wrote: >> > say i have this definition: >> >> > 1 typedef struct SDL_Surface { >> > 2 Uint32 flags; /* Read-only */ >> > 3 SDL_PixelFormat *format; /* Read-only */ >> > 4 int w, h; /* Read-only */ >> > 5 Uint16 pitch; /* Read-only */ >> > 6 void *pixels; /* Read-write */ >> > 7 SDL_Rect clip_rect; /* Read-only */ >> > 8 int refcount; /* Read-mostly */ >> > 9 >> > 10 /* This structure also contains private fields not shown here >> > */ >> > 11 } SDL_Surface; >> >> > notice two pointers, format and pixels. >> > say format has this definition. >> >> > 1 typedef struct { >> > 2 SDL_Palette *palette; >> > 3 Uint8 BitsPerPixel; >> > 4 Uint8 BytesPerPixel; >> > 5 Uint8 Rloss, Gloss, Bloss, Aloss; >> > 6 Uint8 Rshift, Gshift, Bshift, Ashift; >> > 7 Uint32 Rmask, Gmask, Bmask, Amask; >> > 8 Uint32 colorkey; >> > 9 Uint8 alpha; >> > 10 } SDL_PixelFormat; >> >> > so say i want to create a mock sdl handle and pass it to some library >> > function that requires an sdl handle. (would it even work? would i >> > need to use an SDL_SWSURFACE?) >> >> > so i make the pixelformat data using struct.pack, and make the surface >> > data using struct.pack, but how do i link the surface data to the >> > pixelformat data? if i just use id() it'll give me the memory address >> > of the "box" for the string and not the string data itself. thanks. >> >> I think you are looking at the wrong module; you need ctypes, not struct. >> >> http://docs.python.org/library/ctypes.html >> >> Peter > > can you (or anybody) tell me how to link one c struct to another using > ctypes? Thx I know it sounds old-fashioned, but the documentation is worth reading. It contains examples for structs, pointers and arrays, e. g. """ >>> from ctypes import * >>> class cell(Structure): .... pass .... >>> cell._fields_ = [("name", c_char_p), .... ("next", POINTER(cell))] >>> """ Peter
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