In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it possible
to make the contents of an unknown address be "allocbuf"? ?
JS
11  1860 
JS wrote: In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it possible
to make the contents of an unknown address be "allocbuf"? ?
It has been set to point to something, allocbuf[] which is a block of
memory. So allocp points to the first element of allocbuf.
> static char *allocp = allocbuf;
^^^^^^^^^
If you look more careful you'll see that allocp has been set to the
start of the array allocbuf. allocbuf is basicly a pointer to the
memorylocation for the array.
--
bjrnove
"Mark Odell" <od*******@hotm ail.com> skrev i en meddelelse
news:39******** *****@individua l.net... JS wrote: In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it
possible to make the contents of an unknown address be "allocbuf"? ?
It has been set to point to something, allocbuf[] which is a block of
memory. So allocp points to the first element of allocbuf.
But should that not be written as:
1) static char *allocp; // declares that *allocp is a pointer to a char.
2) allocp = &allocbuf[0]; // makes allocp point to the first address in
allocbuf.
3) allocp = allocbuf; // the same as 2) just a short hand.
Then I can write:
*allocp = allocbuf;
which means that the contents of the address that allocp is pointing at is
the first element of allocbuf.
JS
JS wrote: "Mark Odell" <od*******@hotm ail.com> skrev i en meddelelse
news:39******** *****@individua l.net...
JS wrote:
In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it
possible
to make the contents of an unknown address be "allocbuf"? ?
It has been set to point to something, allocbuf[] which is a block of
memory. So allocp points to the first element of allocbuf.
But should that not be written as:
1) static char *allocp; // declares that *allocp is a pointer to a char.
2) allocp = &allocbuf[0]; // makes allocp point to the first address in
allocbuf.
3) allocp = allocbuf; // the same as 2) just a short hand.
Then I can write:
*allocp = allocbuf;
which means that the contents of the address that allocp is pointing at is
the first element of allocbuf.
Can be. There is a convenient shortcut you can take during definition,
that is, you can initialze at the definition point. E.g.
int value = 12;
int *pValue = &value;
char allocbuf[1024];
char *pAllocbuf = allocbuf; /* or &allocbuf[0] if you wish */
Do not confuse this with assignment (not the same as initialization)
like this:
*pAllocbuf = allocbuf; /* Error! */
Okay?
- Mark
On Wed, 16 Mar 2005 15:52:23 +0100, JS wrote: In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it possible
to make the contents of an unknown address be "allocbuf"? ?
Your second line has an initialiser for allocp. It is saying that allocp
is a static variable of type char * and its initial value is (a
pointer to the first element of) allocbuf. The initialisation is broadly
equivalent to the assignment (executed sometime before the program starts):
allocp = allocbuf;
it is NOT equivalent to
*allocp = allocbuf;
Lawrence
"Mark Odell" <od*******@hotm ail.com> skrev i en meddelelse
news:39******** *****@individua l.net... JS wrote: "Mark Odell" <od*******@hotm ail.com> skrev i en meddelelse
news:39******** *****@individua l.net...
JS wrote:
In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it
possible
to make the contents of an unknown address be "allocbuf"? ?
It has been set to point to something, allocbuf[] which is a block of
memory. So allocp points to the first element of allocbuf.
But should that not be written as:
1) static char *allocp; // declares that *allocp is a pointer to a char.
2) allocp = &allocbuf[0]; // makes allocp point to the first address in
allocbuf.
3) allocp = allocbuf; // the same as 2) just a short hand.
Then I can write:
*allocp = allocbuf;
which means that the contents of the address that allocp is pointing at
is the first element of allocbuf.
Can be. There is a convenient shortcut you can take during definition,
that is, you can initialze at the definition point. E.g.
int value = 12;
int *pValue = &value;
char allocbuf[1024];
char *pAllocbuf = allocbuf; /* or &allocbuf[0] if you wish */
This last line implies pAllocbuf = allocbuf..right ?
But is it the value at allocbuf[0] or is it the address?
JS wrote: >In K&R I have found this:
>
>static char allocbuf[ALLOCSIZE];
>static char *allocp = allocbuf;
>
>But *allocp has not been set to point at anything yet so how is it
possible
>to make the contents of an unknown address be "allocbuf"? ?
It has been set to point to something, allocbuf[] which is a block of
memory. So allocp points to the first element of allocbuf.
But should that not be written as:
1) static char *allocp; // declares that *allocp is a pointer to a char.
2) allocp = &allocbuf[0]; // makes allocp point to the first address in
allocbuf.
3) allocp = allocbuf; // the same as 2) just a short hand.
Then I can write:
*allocp = allocbuf;
which means that the contents of the address that allocp is pointing at
is
the first element of allocbuf.
Can be. There is a convenient shortcut you can take during definition,
that is, you can initialze at the definition point. E.g.
int value = 12;
int *pValue = &value;
char allocbuf[1024];
char *pAllocbuf = allocbuf; /* or &allocbuf[0] if you wish */
This last line implies pAllocbuf = allocbuf..right ?
It doesn't imply it, C says that it will initialize pAllocbuf to point
to allocbuf just as if you had written:
pAllocbuf = allocbuf;
So I guess your statement is correct.
But is it the value at allocbuf[0] or is it the address?
pAllocbuf will contain the address of allocbuf[0], e.g. &allocbuf[0] and
*pAllocbuf will contain the value held in allocbuf[0].
--
- Mark
"Lawrence Kirby" <lk****@netacti ve.co.uk> skrev i en meddelelse
news:pa******** *************** *****@netactive .co.uk... On Wed, 16 Mar 2005 15:52:23 +0100, JS wrote:
In K&R I have found this:
static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;
But *allocp has not been set to point at anything yet so how is it
possible to make the contents of an unknown address be "allocbuf"? ?
Your second line has an initialiser for allocp. It is saying that allocp
is a static variable of type char * and its initial value is (a
pointer to the first element of) allocbuf. The initialisation is broadly
equivalent to the assignment (executed sometime before the program
starts):
allocp = allocbuf;
it is NOT equivalent to
*allocp = allocbuf;
In the book they say that:
static char *allocp = allocbuf;
is equivalent with:
static char *allocp = &allocbuf[0];
with I assume is also equivalent with:
static char allocp = allocbuf;
"JS" <sf****@asdas.c om> writes: In the book they say that:
static char *allocp = allocbuf;
is equivalent with:
static char *allocp = &allocbuf[0];
Yes. If allocbuf is an array of char or a pointer to char, both
are valid and equivalent.
with I assume is also equivalent with:
static char allocp = allocbuf;
No. Given the same assumption, this code requires a diagnostic
because it implicitly converts from a pointer type to a character
type.
--
"In My Egotistical Opinion, most people's C programs should be indented six
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