Simple problem with pointers

[mark]

Hello,

I have two variables:
bool oldValues[2] = {true, false};
bool newValues[2] = {false, false};

Now I would like to copy to oldValues the values from newValues. I
don't want to copy it one by one (using for) but just copy the address
in memory which points to newValues into oldValues. How can I do that?

btw. Is it possible to inicialize such array in the presented way (i.e.
using = {true, false} ) after initialisation, i..e bool values[2];
values = {true, false} doesn't work, but maybe there is another way to
do it without for)??

Thank you very much, marko

[Walter Roberson]

In article <11*********************@73g2000cwn.googlegroups.c om>,
mark <mk*********@gmail.comwrote:

>I have two variables:
bool oldValues[2] = {true, false};
bool newValues[2] = {false, false};

>Now I would like to copy to oldValues the values from newValues. I
don't want to copy it one by one (using for) but just copy the address
in memory which points to newValues into oldValues. How can I do that?

You cannot. Once an array is declared, you should consider its
address to be constant (i.e., unchangable) within its execution lifetime.

>btw. Is it possible to inicialize such array in the presented way (i.e.
using = {true, false} ) after initialisation, i..e bool values[2];
values = {true, false}

No.

>doesn't work, but maybe there is another way to
do it without for)??

If you were using a structure, there is structure assignment.
For arrays, there is no mass assignment as such, but there is
memcpy()
--
Programming is what happens while you're busy making other plans.

[Ben Pfaff]

"mark" <mk*********@gmail.comwrites:

I have two variables:
bool oldValues[2] = {true, false};
bool newValues[2] = {false, false};

Now I would like to copy to oldValues the values from newValues. I
don't want to copy it one by one (using for) but just copy the address
in memory which points to newValues into oldValues. How can I do that?

It sounds like you should read section 6, "Arrays and Pointers",
in the C FAQ.
--
Ben Pfaff
email: bl*@cs.stanford.edu
web: http://benpfaff.org

[Richard]

ro******@ibd.nrc-cnrc.gc.ca (Walter Roberson) writes:

In article <11*********************@73g2000cwn.googlegroups.c om>,
mark <mk*********@gmail.comwrote:

>>I have two variables:
bool oldValues[2] = {true, false};
bool newValues[2] = {false, false};

>>Now I would like to copy to oldValues the values from newValues. I
don't want to copy it one by one (using for) but just copy the address
in memory which points to newValues into oldValues. How can I do that?

You cannot. Once an array is declared, you should consider its
address to be constant (i.e., unchangable) within its execution
lifetime.

Reading between the lines I would guess he doesn't want to change the
address of the arrays : he wants to "quickly" copy the contents of one
into the other in some sort of fast memory copy.

>

>>btw. Is it possible to inicialize such array in the presented way (i.e.
using = {true, false} ) after initialisation, i..e bool values[2];
values = {true, false}

No.

>>doesn't work, but maybe there is another way to
do it without for)??

If you were using a structure, there is structure assignment.
For arrays, there is no mass assignment as such, but there is
memcpy()

Agreed, possibly he is looking for a memcpy solution?

Something along the lines of

memcpy(oldValues,newValues,sizeof(oldValues));

?

[sam_cit]

>

Agreed, possibly he is looking for a memcpy solution?

Something along the lines of

memcpy(oldValues,newValues,sizeof(oldValues));

?

This holds true that the values are stored in consequtive memory
locations, however i remember that data structure for an array doesn't
expect it to be consequtive, rather they indicate a mapping between the
memory location of the individual elements of the array and a key and
it is that the key is stored in a consequtive memory locations, i know
that this sounds like an array of pointers to any type, but i really
wonder what should be an ideal implementation for an array, any
comments???

[Nick Keighley]

sa*****@yahoo.co.in wrote:

Agreed, possibly he is looking for a memcpy solution?

Something along the lines of

memcpy(oldValues,newValues,sizeof(oldValues));

?

This holds true that the values are stored in consequtive memory
locations,

they are, though there may be padding between the items.

forall i: &a[i] < &a[i+1]

however i remember that data structure for an array doesn't
expect it to be consequtive, rather they indicate a mapping between the
memory location of the individual elements of the array and a key and
it is that the key is stored in a consequtive memory locations,

no.

i know
that this sounds like an array of pointers to any type, but i really
wonder what should be an ideal implementation for an array, any
comments???

a simple set of strictly increasing memory addresses. The memcpy()
above is completly correct.
--
Nick Keighley

"Half-assed programming was a time-filler that, like knitting,
must date to the beginning of human experience."
"A Fire Upon The Deep" by Verne Vinge

[Keith Thompson]

"Nick Keighley" <ni******************@hotmail.comwrites:

sa*****@yahoo.co.in wrote:

Agreed, possibly he is looking for a memcpy solution?

Something along the lines of

memcpy(oldValues,newValues,sizeof(oldValues));

?

This holds true that the values are stored in consequtive memory
locations,

they are, though there may be padding between the items.

forall i: &a[i] < &a[i+1]

[...]

No, there is no padding between elements of an array.

This implies, among other things, that any type's size must be a
multiple of its alignment.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.