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gregd

Memory Allocation problem

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gregd    122
The problem I'm facing now is, when I pass a struct pointer, to a function, and try to allocate memory with malloc for it, from inside of that function, it doesn't seem to allocate memory to the struct I was passing to this function. malloc doesn't return NULL, so, it did allocate some data. but after calling the function (ptr_structdata[(i)] == NULL), where i is just an index into the struct. (i allocate a few structs actually...its an array, that might be the problem, but im not sure) however, when i pass the pointer to that function by reference, it seems to work. what could be wrong? --- here is the code:

// doesnt work:
void REF_MallocItemPointer (ref_item_t *dataptr, int datacount)
{
	if ( (dataptr = (ref_item_t *) malloc ((REF_ITEM_HEADER_SIZE + 4) * datacount)) == NULL )
	LogErr("; REF_MallocItem: insufficient memory!\n");
}

// works:
void REF_MallocItemReference (ref_item_t &dataptr, int datacount)
{
	if ( (dataptr =
		 (ref_item_t *) malloc ((REF_ITEM_HEADER_SIZE + 4) * datacount)) == NULL)
			LogErr("; REF_Build: malloc: insufficient memory!\n");
}

typedef struct tagItem
{
	char	ri_name[8];			// 8-char name derived from the filename
	dword	ri_size;			// size of the header + all data, in bytes
	dword	ri_type;			// REF_PIC, REF_FONT, REF_TEXT, ...
	word	ri_width;			// 
	word	ri_height;

	word	ri_data_type;		// REF_8BIT, REF_24BIT, REF_16BIT, REF_32BIT
	word	ri_data_flag;		// 
	void   *ri_data;			// data
} ref_item_t;


ref_item_t *REF_ITEM;

// WORKS:
REF_MallocItemReference (*REF_ITEM, 2);

pseudo: at this point, REF_ITEM[0] != NULL;


// DOESN'T WORK:
REF_MallocItemPointer (REF_ITEM, 2);

pseudo: at this point, REF_ITEM[0] == NULL;



As you can see, im actually using the asterisk to "dereference" a pointer, so that the reference of the data is passed to the function 

[edited by - gregd on April 30, 2003 11:29:22 PM]    

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Sneftel    1788
you''re passing the pointer by value. Remember? When you pass an argument, a copy of it is made when it is passed into the function. You need to use either a reference to a pointer (in C++), or a pointer to a pointer. Assuming you do the second, your call would look like *dataptr = malloc(stuff).


How appropriate. You fight like a cow.

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