Which is the correct way, to initialise a pointer to an element of
an array. I am sorry if my terminology is not correct
/* declare pointer */
int *ptr;
/* define and initialise array */
int array[10] = {,0,1,2,3,4,5,6 ,7,8,9};
/* assign value to pointer */
ptr = &array[9]; or ptr = (array + 9);
I have found both work but to avoid future problems is one
better than the other. And if so why
Nov 14 '05
12 6261
Christopher Benson-Manica wrote: Eric <eg************ *@verizon.net> spoke thus: darklight <ng******@netsc apel.net> wrote:
/* declare pointer */ int *ptr; /* define and initialise array */ int array[10] = {0,1,2,3,4,5,6, 7,8,9}; ^ extra comma removed /* assign value to pointer */ ptr = &array[9]; or ptr = (array + 9);
Either one works equally well and the decision on which to use is generally based on personal preference and the context.
But the equivalence breaks down for
ptr=array+10; /* Legal */ ptr=&array[10]; /* Illegal (?), since array[10] is a dereference */
, right?
Wrong, at least in C99.
[6.5.3.2]
3 The unary & operator returns the address of its operand. [...]
Similarly, if the operand is the result of a [] operator, neither
the & operator nor the unary * that is implied by the [] is
evaluated and the result is as if the & operator were removed and
the [] operator were changed to a + operator.
Jeremy.
Jeremy Yallop <je****@jdyallo p.freeserve.co. uk> spoke thus: 3 The unary & operator returns the address of its operand. [...] Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator.
Thank you, I am yet again abashed yet wiser :)
--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.
In article <cd************ ************@po sting.google.co m>, an********@yaho o.co.in (Anand) wrote: Hi
ptr=&array[9] 0r (array+9) both refer same operation.
You should have just stopped there.
The basic difference is that by accessing with pointers the operation will be quite faster while comparing array[9].
Says who? I have *never* seen a compiler that generates more efficent
code for (&array[9]) than it does for *(array+9). This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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http://home.no.net/dubjai/win32cpptut/special/pointers/ch_01_examples.zip
To access the table of contents, use the "Bookmarks" tab in Adobe
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