The difference between char a[6] and char *p=new char[6] ?

W

wwj

Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6] and the difference between the heap and the stack ,and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Give me some hint.
THANK YOU.
 
C

Christian Bau

Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6] and the difference between the heap and the stack ,and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Could you have a very very close look at the name of the newsgroup you
are posting to? Is the name of that newsgroup "comp.lang.c++"? If not,
then you are posting your C++ questions to the wrong newsgroup.
 
B

Bruno Desthuilliers

wwj said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6]

The difference is that the second statement has no meaning in C.
C++ is the second group down the hall, on the the left...
and the difference between the heap and the stack,

This has nothing to do with the C language.
and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Since the C language has no notion of stack or heap, and since the
second statement has no meaning in C, we can't answer such a question.
Give me some hint.

first hint : C and C++ are two different languages. please post on the
appropriate newsgroup.

second hint :

#include <regulars_please_correct_me_if_necessary.h>

C <ot>and C++</ot> have a notion of automatic memory and a notion of
dynamic memory.

Automatic memory is the default storage, and local variables are usually
automatic. This means that memory is automatically allocated for these
variable at the beginning of the block, and that this memory is
automatically freed at the end of the block.

Automatic memory *may* be, on *some* platforms, implemented with a stack.

Dynamic memory is memory that is allocated on demand, with a special
mechanism (in C, usually the 'malloc()' function, <ot>in C++ usually the
'new' operator</ot>), and that must be freed by code - usually in C with
the 'free()' function <ot>and in C++ with 'delete'</ot>). Not freeing
dynamically allocated memory (usually) causes a 'memory leak'.

Dynamic memory *may* be, on *some* platforms, implemented with a 'heap'.

Third hint : please learn the difference between C and C++, choose the
one you like, get yourself a *good* book on it, and post on the
appropriate group - after you've read the group's FAQ.
THANK YOU.
Please dont scream, it's hurting my ears.

Bruno
 
W

wwj

......~~
Christian Bau said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6] and the difference between the heap and the stack ,and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Could you have a very very close look at the name of the newsgroup you
are posting to? Is the name of that newsgroup "comp.lang.c++"? If not,
then you are posting your C++ questions to the wrong newsgroup.
 
W

wwj

Bruno ,Anyway firstly I thank you ,it's my wrong to post it here and
now yet I can not tell from c and c++ well. Then,I want to say that
our world is developing ,all developing,and the language c not be
invent from uk or by you or Christian Bau,ple you do not regulate(this
word not proper) it or sneer at others (new one) or rave at others .
Bruno Desthuilliers said:
wwj said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6]

The difference is that the second statement has no meaning in C.
C++ is the second group down the hall, on the the left...
and the difference between the heap and the stack,

This has nothing to do with the C language.
and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Since the C language has no notion of stack or heap, and since the
second statement has no meaning in C, we can't answer such a question.
Give me some hint.

first hint : C and C++ are two different languages. please post on the
appropriate newsgroup.

second hint :

#include <regulars_please_correct_me_if_necessary.h>

C <ot>and C++</ot> have a notion of automatic memory and a notion of
dynamic memory.

Automatic memory is the default storage, and local variables are usually
automatic. This means that memory is automatically allocated for these
variable at the beginning of the block, and that this memory is
automatically freed at the end of the block.

Automatic memory *may* be, on *some* platforms, implemented with a stack.

Dynamic memory is memory that is allocated on demand, with a special
mechanism (in C, usually the 'malloc()' function, <ot>in C++ usually the
'new' operator</ot>), and that must be freed by code - usually in C with
the 'free()' function <ot>and in C++ with 'delete'</ot>). Not freeing
dynamically allocated memory (usually) causes a 'memory leak'.

Dynamic memory *may* be, on *some* platforms, implemented with a 'heap'.

Third hint : please learn the difference between C and C++, choose the
one you like, get yourself a *good* book on it, and post on the
appropriate group - after you've read the group's FAQ.
THANK YOU.
Please dont scream, it's hurting my ears.

Bruno
 
J

Joona I Palaste

wwj said:
Bruno ,Anyway firstly I thank you ,it's my wrong to post it here and
now yet I can not tell from c and c++ well. Then,I want to say that
our world is developing ,all developing,and the language c not be
invent from uk or by you or Christian Bau,ple you do not regulate(this
word not proper) it or sneer at others (new one) or rave at others .

In other words, because neither Bruno or Christian invented C, this
newsgroup can freely be abused by posting off-topic messages which don't
concern C at all?
 
D

Default User

wwj said:
Bruno ,Anyway firstly I thank you ,it's my wrong to post it here and
now yet I can not tell from c and c++ well. Then,I want to say that
our world is developing ,all developing,and the language c not be
invent from uk or by you or Christian Bau,ple you do not regulate(this
word not proper) it or sneer at others (new one) or rave at others .


Don't top-post. Your replies belong following properly trimmed quotes.


This newsgroup has topicality guidelines, which will be enforced by all
the regulars. Those two happened to be the first to correct you, others
would certainly have if they hadn't.

I suggest you apologize to the group and the two individuals for your
poor behavior.




Brian Rodenborn
 
C

CBFalconer

Joona said:
In other words, because neither Bruno or Christian invented C, this
newsgroup can freely be abused by posting off-topic messages which don't
concern C at all?

wwj obviously has a language barrier, and is doing his/her best.
So there is no need to pick at him. Simply drop it, and see what
develops. He already explained he doesn't know the difference
between C and C++, and obviously has not been told to lurk before
posting.
 
R

Roose

Don't mind them, see some of the other threads:

Asking if elements in struct arre zero
"Mastering C Pointers"....
Interview question !!!
ANSI C compliance

for a discussion of why you got jumped on so harshly. It is unfortunate
that people are so rude to someone just seeking an answer to a simple
question. One (non-sarcastic) post pointing out that it's off-topic is
quite enough. No need for a pathetic display of severe personality defects.

But yes your post has to do with C++, so unfortunately you won't get a good
answer here. But let me try, to make up for the harsh treatment (flames be
gone, it's off-topic anyway):

char a[6], if declared in a function, is a character array on the stack,
typically (flamers note: if I go into auto, it's going to take a lot more
explanation than he cares to hear, so STFU)

char *p = new char[6]; assigns to p a pointer to the beginning of 6
bytes of dynamically allocated memory, typically located on the "heap" as
you said

Google for "stack" and some other stuff maybe "function" "compiler", if you
don't know what a stack is. It's an abstract data type, and can be used to
implement variables declared in a function in C. That is, it manages their
automatic cleanup after the function exits. In contrast, you must
explicitly call "delete p" in order to free the memory allocated by new --
otherwise you have a memory leak.

The difference is that they are basically different systems of managing
memory. With a stack, you don't have to worry about cleaning up -- however
the variable has limited scope. A variable on the heap persists as long as
you need it, and you take responsibility for cleaning it up yourself.

Roose
 
R

Richard Heathfield

Roose wrote:

But yes your post has to do with C++, so unfortunately you won't get a
good
answer here.

He will, however, get a good answer in comp.lang.c++
But let me try, to make up for the harsh treatment (flames
be gone, it's off-topic anyway):

Not only will he get a good answer in comp.lang.c++ but, also, any mistakes
in that answer will stand a much better chance of correction if it is
presented in the correct newsgroup.

char a[6], if declared in a function, is a character array on the
stack,

That is not necessarily true.
char *p = new char[6]; assigns to p a pointer to the beginning of 6
bytes of dynamically allocated memory, typically located on the "heap" as
you said

No, it's a syntax error in C, which is the topic of this newsgroup.

<snip>
 
W

wwj

Ok,thanks Roose very much.You are a good person , goodness.

In our here ,I learn from school that basiclly C++ is a extension of
C,and C is a subset of C++,expcept some difference.Maybe it is that my
teacher do not express that clearly or I do not understand that
clearly.So sorry for everyone ,I wish this post ends the heartrending
topic,and all not waster time on the confused quarrel.
Roose said:
Don't mind them, see some of the other threads:

Asking if elements in struct arre zero
"Mastering C Pointers"....
Interview question !!!
ANSI C compliance

for a discussion of why you got jumped on so harshly. It is unfortunate
that people are so rude to someone just seeking an answer to a simple
question. One (non-sarcastic) post pointing out that it's off-topic is
quite enough. No need for a pathetic display of severe personality defects.

But yes your post has to do with C++, so unfortunately you won't get a good
answer here. But let me try, to make up for the harsh treatment (flames be
gone, it's off-topic anyway):

char a[6], if declared in a function, is a character array on the stack,
typically (flamers note: if I go into auto, it's going to take a lot more
explanation than he cares to hear, so STFU)

char *p = new char[6]; assigns to p a pointer to the beginning of 6
bytes of dynamically allocated memory, typically located on the "heap" as
you said

Google for "stack" and some other stuff maybe "function" "compiler", if you
don't know what a stack is. It's an abstract data type, and can be used to
implement variables declared in a function in C. That is, it manages their
automatic cleanup after the function exits. In contrast, you must
explicitly call "delete p" in order to free the memory allocated by new --
otherwise you have a memory leak.

The difference is that they are basically different systems of managing
memory. With a stack, you don't have to worry about cleaning up -- however
the variable has limited scope. A variable on the heap persists as long as
you need it, and you take responsibility for cleaning it up yourself.

Roose



wwj said:
why?why apologize for my poor behavior ?what is my poor behavior?
Default User <[email protected]> wrote in message
 
R

Richard Bos

(e-mail address removed) (wwj) wrote:

[ Don't top-post, please. Corrected. ]
Roose said:
char a[6], if declared in a function, is a character array on the stack,
typically (flamers note: if I go into auto, it's going to take a lot more
explanation than he cares to hear, so STFU)

The point is that "automatic memory" is a higher-level concept, and
therefore more useful to the reliable, foresightful programmer than "on
the stack". In particular, automatic memory has properties that a stack
need not have, and vice versa.
Besides, automatic memory need not be kept in any stack. It's quite
common, for example, for the smaller auto objects to reside in
registers. Well-written C doesn't care about the difference, as long as
auto objects function as the Standard says they should.
char *p = new char[6]; assigns to p a pointer to the beginning of 6
bytes of dynamically allocated memory, typically located on the "heap" as
you said

Google for "stack" and some other stuff maybe "function" "compiler", if you
don't know what a stack is. It's an abstract data type,

Not in this context, it isn't. _If_ automatic memory is placed in a
stack, it's almost certainly a hardware one. Of course, it would be
possible to write a C implementation for a LISP machine which puts its
auto memory in a software stack, which would be an example of an ADT
after all... and a well-written C program wouldn't care a jot about his
detail.

Erm, no. The demands of automatic memory do that. That's why it's called
"automatic", see? Internally, the C implementation does a lot of byte
shuffling whether your auto memory is on a stack or not; but the point
is that this is hidden from you no matter how it is implemented.

YM duration. Memory has no scope, identifiers have scope. It _is_
possible to have allocated memory, with only one identifier pointing to
it which has block scope, but with allocated duration which lasts beyond
that scope - and this knowledge is important, because failure to
recognise it often causes memory leaks. Like this:

{
int *a;
a=malloc(100* sizeof *a);
}

Note that the pointer a has a scope of no larger than this single block
- yet the memory it is made to point to has a duration beyond the
block's execution time. In this case, this causes a memory leak. A
single return a;, which affects neither the scope of the identifier nor,
strictly speaking, the duration of the object, could solve the leak.
Ok,thanks Roose very much.You are a good person , goodness.

I doubt that. His information, in any case, is dubious.
In our here ,I learn from school that basiclly C++ is a extension of
C,and C is a subset of C++,expcept some difference.

That is, alas, a much-held view, but it's wrong. _Good_ C++ is
fundamentally different from good C. It is, indeed, possible to write a
restricted kind of C++ which looks like a restricted kind of C, but in
the general case the result will be bad C, and AFAICT worse C++.
Maybe it is that my teacher do not express that clearly

All too many teachers don't know what the blazes they are on about, and
all too many teachers do indeed think that they know C == C++ minus
classes, which is patently and obviously false.

Richard
 
B

Bruno Desthuilliers

wwj wrote:

[OT] Please don't top-post (corrected)
Bruno Desthuilliers said:
wwj said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6]

The difference is that the second statement has no meaning in C.
C++ is the second group down the hall, on the the left...
(snip)
This has nothing to do with the C language.
> Bruno ,Anyway firstly I thank you ,it's my wrong to post it here and
> now yet I can not tell from c and c++ well.

They are two distinct languages, even if they share some common parts.
C++ as been designed to be as compatible as possible with the C language
as it was by the time, so some C source may be compiled in C++ as is or
with little modification, but still they are really two distinct languages.
> Then,I want to say that
> our world is developing ,all developing,and the language c not be
> invent from uk or by you or Christian Bau,

None of us three would claim to have invented this language.
>ple you do not regulate(this
> word not proper) it

As regular readers (me) or regular posters (some other here) of this
newsgroup, we do regulate it in order to keep a good signal/noise ratio.
This (auto) regulation makes this group one of the best places around to
learn C.
>or sneer at others (new one) or rave at others .

Ok, it's usenet here and we usually go straight to the point. I
understand this may seem a bit harsh at first, but you'd better get used
to it !-)

According to the usenet standards, I think that my answer was quite
polite, as I did take the time to explain why you were OT here and even
tried to partially answer your question and give you some useful hints.

Bruno
 
G

Guest

wwj said:
i have said its my wrong to post it here !!!!!!!

These people don't care.

You made an error (or errors) and now must be punished because you are
not in the inner circle (http://tinyurl.com/8qpp). They make these same
(non-C related) errors, but would never go after each other the same way
they go after others.

I would suggest that in the future you just ignore them when their
comments refer to anything other then the C language or don't directly
answer your question.

However, they are quite knowledgeable about C and you should feel free
to use this group to extract that knowledge whenever you feel the need.

--
 
C

CBFalconer

wwj said:
In our here ,I learn from school that basiclly C++ is a extension
of C,and C is a subset of C++,expcept some difference.Maybe it is
that my teacher do not express that clearly or I do not understand
that clearly.So sorry for everyone ,I wish this post ends the
heartrending topic,and all not waster time on the confused quarrel.

You are still topposting, which means adding your answer
**before** the quoted text. Your reply goes **after** any quoted
text (or possibly intermixed), so that things read in a logical
order. You should also snip any quotations not germane to your
reply.

Topposting is considered extremely rude in the better newsgroups,
of which this is one.

To correct a misconception, C++ is a different language than C. C
is NOT a subset. If your teacher is telling you otherwise he is
flat out WRONG. You may quote me to him if you wish, as it may
not be politic to contradict him yourself.
 
M

Minti

Bruno Desthuilliers said:
wwj said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6]

The difference is that the second statement has no meaning in C.
C++ is the second group down the hall, on the the left...
and the difference between the heap and the stack,

This has nothing to do with the C language.
and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Since the C language has no notion of stack or heap, and since the
second statement has no meaning in C, we can't answer such a question.
Give me some hint.

first hint : C and C++ are two different languages. please post on the
appropriate newsgroup.

second hint :

#include <regulars_please_correct_me_if_necessary.h>

C <ot>and C++</ot> have a notion of automatic memory and a notion of
dynamic memory.

Automatic memory is the default storage, and local variables are usually
automatic. This means that memory is automatically allocated for these
variable at the beginning of the block, and that this memory is
automatically freed at the end of the block.

Automatic memory *may* be, on *some* platforms, implemented with a stack.

Dynamic memory is memory that is allocated on demand, with a special
mechanism (in C, usually the 'malloc()' function, <ot>in C++ usually the
'new' operator</ot>), and that must be freed by code - usually in C with
the 'free()' function <ot>and in C++ with 'delete'</ot>). Not freeing
dynamically allocated memory (usually) causes a 'memory leak'.

Dynamic memory *may* be, on *some* platforms, implemented with a 'heap'.

Third hint : please learn the difference between C and C++, choose the
one you like, get yourself a *good* book on it, and post on the
appropriate group - after you've read the group's FAQ.

Wrong there are 3 types of memory in C and C++

1) Automatic
2) Dynamic
3 and Static
 
M

Minti

These people don't care.

You made an error (or errors) and now must be punished because you are
not in the inner circle (http://tinyurl.com/8qpp). They make these same
(non-C related) errors, but would never go after each other the same way
they go after others.

I would suggest that in the future you just ignore them when their
comments refer to anything other then the C language or don't directly
answer your question.

However, they are quite knowledgeable about C and you should feel free
to use this group to extract that knowledge whenever you feel the need.

--

Wow you seem to allow all those 'killer bees' who just want to suck
you for their own good. Thank you very much. This is a community. In
every community be it dog or cat or lion or tiger or even human we
tend to protect members of community. Look around you and see how many
peopled do YOU listen too.

"Hello my name is Imanpreet?"

Will you respond..
 
M

Mike Wahler

Minti said:
Bruno Desthuilliers <[email protected]> wrote in message
wwj said:
Hi ,all

I want to know the difference between char a[6] and char *p=new
char[6]

The difference is that the second statement has no meaning in C.
C++ is the second group down the hall, on the the left...
and the difference between the heap and the stack,

This has nothing to do with the C language.
and if the
char a[6] is corresponding to the stack in MEMORY,and char *p=new
char[6] is corresponding to the heap of MEMORY.

Since the C language has no notion of stack or heap, and since the
second statement has no meaning in C, we can't answer such a question.
Give me some hint.

first hint : C and C++ are two different languages. please post on the
appropriate newsgroup.

second hint :

#include <regulars_please_correct_me_if_necessary.h>

C <ot>and C++</ot> have a notion of automatic memory and a notion of
dynamic memory.

Automatic memory is the default storage,

In block scope. Storage defined at file scope is has static
storage duration by definition.
and local variables are usually

Wrong there are 3 types of memory

That's 'storage duration'.
in C and C++

1) Automatic
2) Dynamic
3 and Static

Yes there are, but I don't think Bruno's message was 'wrong'.

The acknowledgement of the existence of apples and oranges
does not imply denial of the existence of bananas. I didn't
see Bruno say 'only' automatic and dynamic (actually the formal
term for the latter is 'allocated' (6.2.4)).

-Mike
 

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