Return ((ulong*) (x)) [-1])

Source: Internet
Author: User
See a function defined as follows: #include "u.h" #include "lib.h" ulong getcallerpc (void *x) {return (((ulong*) (x)) [-1]);} ((ulong*) (x)) to cast the void* X-pin to ulong*

You can now understand that X points to an array of ulong types
[-1]: Indicates the element to go before X

The code above is equivalent to the

ULONG px= (ulong*) x
--px
Return (*PX)

In general, the following table-1 is not used, and it is estimated that there is any special usage here, which depends on how it is actually used.

------------------------------------------------------------------------
ULONG Getcallerpc (void *x)
{
Return ((ulong*) (x)) [-1]);
}

In ((ulong*) (x)) [-1]:
X is a pointer
(ulong*) (x): Converts an X to a ulong type pointer, and we assume that (ulong*) (x) after conversion, the pointer is Y, then
((ulong*) (x)) [-1] is: y[-1], and y[-1] points to the address in front of the first address of Y. This situation is only
When you know what the address is, that's the special usage upstairs. ~_~

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