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matrix pointer

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# 1  
Old 03-02-2009
matrix pointer
Can anyone tell me what the following statements do?
float (*tab)[MAXCLASS];
tab=(float (*)[MAXCLASS]) calloc(MAXCLASS,
(MAXCLASS+1)*sizeof(float));
# 2  
Old 03-02-2009
Code:
/* creates a pointer named tab that points to an array of MAXCLASS items of type float */
float (*tab)[MAXCLASS];

/* 
  allocates memory for MAXCLASS elements each of size (MAXCLASS+1)*sizeof(float) bytes and
  initializes all memory locations to zeros and casts the pointer to the appropriate type
 */
tab=(float (*)[MAXCLASS]) calloc(MAXCLASS, (MAXCLASS+1)*sizeof(float));

The last one allocates too much memory and IMO the calloc should be...
Code:
/*
  allocates memory for MAXCLASS elements each of sizeof(float) bytes and sets
  the memory locations to zeros and casts the pointer to the appropriate type
 */
tab=(float (*)[MAXCLASS]) calloc(MAXCLASS, sizeof(float));

# 3  
Old 03-02-2009
Forgot to add that though the two statements are equivalent their difference is that this one allocates memory on the stack...
Code:
float (*tab)[MAXCLASS];

while the one below allocates memory from the heap...
Code:
tab=(float (*)[MAXCLASS]) calloc(MAXCLASS, (MAXCLASS+1)*sizeof(float));

and written as is the heap one uses more memory than the stack one unless written as shown in my previous post.
# 4  
Old 03-03-2009
Thanks very much.
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