Little problem with pointer

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Little problem with pointer #313792 03/03/10 17:28 03/03/10 17:28
Joined: Jun 2004 Posts: 655 to your left BoH_Havoc OP User
BoH_Havoc OP User Joined: Jun 2004 Posts: 655 to your left	I have a small(?) problem here: Code: typedef struct { VECTOR3D n; float d; } Plane; typedef struct { Plane* plane; int size; } VecPlane; void planesSetSize(VecPlane* p, const int csize) { if (p != NULL) { if (csize != p->size) { p->plane = (Plane)realloc(p->plane, csizesizeof(Plane)); p->size = csize; } } } when compiling i get Quote: "can not convert 'POINTER' to 'struct Plane'" for p->plane = (Plane)realloc(p->plane, csizesizeof(Plane)); and Quote: illegal indirection for p->size = csize; Tried a lot of combinations with () and * but so far none worked Any help appreciated Shade-C EVO Lite-C Shader Framework

Re: Little problem with pointer [Re: BoH_Havoc] #313795 03/03/10 17:36 03/03/10 17:36
Joined: Nov 2007 Posts: 1,143 United Kingdom DJBMASTER Serious User
DJBMASTER Serious User Joined: Nov 2007 Posts: 1,143 United Kingdom	Code: p->plane = (Plane)realloc(p->plane, csizesizeof(Plane)); p->size = csize; I think this is your problem. You dereference the pointer, and then use the 'member-by-pointer' operator, when you really want a 'member-by-variable'. So just remove the * ... Code: p->plane = (Plane)realloc(p->plane, csizesizeof(Plane)); p->size = csize; or (p).plane = (Plane)realloc(p->plane, csizesizeof(Plane)); (p).size = csize; Last edited by DJBMASTER; 03/03/10 17:38.

Re: Little problem with pointer [Re: DJBMASTER] #313798 03/03/10 17:43 03/03/10 17:43
Joined: Jun 2004 Posts: 655 to your left BoH_Havoc OP User
BoH_Havoc OP User Joined: Jun 2004 Posts: 655 to your left	HMmm...but if i remove the , will the original p be altered ? VecPlane orgP; planesSetSize(orgP, 10); is orgP = p from the function now? scratches his head* thanks for the quick reply Shade-C EVO Lite-C Shader Framework

Re: Little problem with pointer [Re: BoH_Havoc] #313802 03/03/10 17:57 03/03/10 17:57
Joined: Nov 2007 Posts: 1,143 United Kingdom DJBMASTER Serious User
DJBMASTER Serious User Joined: Nov 2007 Posts: 1,143 United Kingdom	In the snippet you posted, no, because it wants a pointer to a struct, not the struct itself, so it probably wont even compile. Your original code is fine it's just you've got a syntax error. You can't use a->b because -> gets the member b from the pointer a, and so by derefencing it, you are turning a into the variable, where -> fails. All this pointer stuff gets confusing after a while, but I think your code is correct except for those 2 lines I posted earlier, where you are mixing with ->. Last edited by DJBMASTER; 03/03/10 17:59.

Re: Little problem with pointer [Re: DJBMASTER] #313845 03/03/10 22:21 03/03/10 22:21
Joined: Dec 2008 Posts: 271 Saturnus Member
Saturnus Member Joined: Dec 2008 Posts: 271	Yeah, DJBMASTER is right here: use the two code lines posted by him. "HMmm...but if i remove the *, will the original p be altered ?" Yes. In lite-C you can't pass structs by value, so p still points to your original struct. "VecPlane orgP; planesSetSize(orgP, 10);" lite-C is supposed to differentiate between objects and pointers automatically (unless you set PRAGMA_POINTER). However, to be on the safe side you should use the address operator here: planesSetSize(&orgP, 10)

Re: Little problem with pointer [Re: Saturnus] #313996 03/04/10 21:42 03/04/10 21:42
Joined: Jun 2004 Posts: 655 to your left BoH_Havoc OP User
BoH_Havoc OP User Joined: Jun 2004 Posts: 655 to your left	Alrighty, thanks a bunch guys! Shade-C EVO Lite-C Shader Framework