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Full Discussion: C pointer/array duality confusion
Top Forums Programming C pointer/array duality confusion Post 302427722 by gorga on Monday 7th of June 2010 03:51:37 PM
Old 06-07-2010
Thanx for your reply,

"you're trying to initialize a struct, from a pointer."

I thought with the typedef...

Code:
typedef section_t* region_t[SECTION_LENGTH];

This would mean that the following statement would be assigning a ptr to a ptr...

Code:
region_t region = ctn.regions[nth];

Because a region_t is a ptr type...or in other words, an array of section_t* ptrs. Hence my confusion, I thought in C an array and a ptr were essentially the same things, so this would work.

Anyway I got it to work by changing the assignment to the following...
Code:
section_t** region = ctn.regions[nth];

I realised that "ctn.regions[nth]" is basically an array without the subscript, which means it's a ptr. And what it points to is a ptr to a "section_t"... voila a ptr to a ptr.

And I can access the section_t* by using the subscript, i.e...

Code:
  region[i]->section_t_data_member = x;

 

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LEARN ABOUT NETBSD

atomic_dec_32_nv

ATOMIC_DEC(3)						   BSD Library Functions Manual 					     ATOMIC_DEC(3)

NAME

     atomic_dec, atomic_dec_32, atomic_dec_uint, atomic_dec_ulong, atomic_dec_ptr, atomic_dec_64, atomic_dec_32_nv, atomic_dec_uint_nv,
     atomic_dec_ulong_nv, atomic_dec_ptr_nv, atomic_dec_64_nv -- atomic decrement operations

SYNOPSIS

     #include <sys/atomic.h>

     void
     atomic_dec_32(volatile uint32_t *ptr);

     void
     atomic_dec_uint(volatile unsigned int *ptr);

     void
     atomic_dec_ulong(volatile unsigned long *ptr);

     void
     atomic_dec_ptr(volatile void *ptr);

     void
     atomic_dec_64(volatile uint64_t *ptr);

     uint32_t
     atomic_dec_32_nv(volatile uint32_t *ptr);

     unsigned int
     atomic_dec_uint_nv(volatile unsigned int *ptr);

     unsigned long
     atomic_dec_ulong_nv(volatile unsigned long *ptr);

     void *
     atomic_dec_ptr_nv(volatile void *ptr);

     uint64_t
     atomic_dec_64_nv(volatile uint64_t *ptr);

DESCRIPTION

     The atomic_dec family of functions decrement (by one) the variable referenced by ptr in an atomic fashion.

     The *_nv() variants of these functions return the new value.

     The 64-bit variants of these functions are available only on platforms that can support atomic 64-bit memory access.  Applications can check
     for the availability of 64-bit atomic memory operations by testing if the pre-processor macro __HAVE_ATOMIC64_OPS is defined.

SEE ALSO

     atomic_ops(3)

HISTORY

     The atomic_dec functions first appeared in NetBSD 5.0.

BSD
								  April 11, 2007							       BSD
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