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

 P: n/a 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. Nov 13 '05 #1
24 Replies

 P: n/a In article <87**************************@posting.google.com >, ww*******@mail2.swjtu.edu.cn (wwj) wrote: 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. Nov 13 '05 #2

 P: n/a wwj wrote: 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 C and C++ 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, in C++ usually the 'new' operator), and that must be freed by code - usually in C with the 'free()' function and in C++ with 'delete'). 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 Nov 13 '05 #3

 P: n/a ......~~ Christian Bau wrote in message news:... In article <87**************************@posting.google.com >, ww*******@mail2.swjtu.edu.cn (wwj) wrote: 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. Nov 13 '05 #4

 P: n/a 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 wrote in message news:<3f***********************@news.free.fr>... wwj wrote: 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 C and C++ 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, in C++ usually the 'new' operator), and that must be freed by code - usually in C with the 'free()' function and in C++ with 'delete'). 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 Nov 13 '05 #5

 P: n/a wwj scribbled the following: 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? -- /-- Joona Palaste (pa*****@cc.helsinki.fi) ------------- Finland --------\ \-- http://www.helsinki.fi/~palaste --------------------- rules! --------/ "You could take his life and..." - Mirja Tolsa Nov 13 '05 #6

 P: n/a wwj wrote: 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 Nov 13 '05 #7

 P: n/a Joona I Palaste wrote: wwj scribbled the following: 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? 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. -- Chuck F (cb********@yahoo.com) (cb********@worldnet.att.net) Available for consulting/temporary embedded and systems. USE worldnet address! Nov 13 '05 #8

 P: n/a i have said its my wrong to post it here !!!!!!! Joona I Palaste wrote in message 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? Nov 13 '05 #9

 P: n/a why?why apologize for my poor behavior ?what is my poor behavior? Default User wrote in message news:<3F***************@boeing.com.invalid>... 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 Nov 13 '05 #10

 P: n/a 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. -- Richard Heathfield : bi****@eton.powernet.co.uk "Usenet is a strange place." - Dennis M Ritchie, 29 July 1999. C FAQ: http://www.eskimo.com/~scs/C-faq/top.html K&R answers, C books, etc: http://users.powernet.co.uk/eton Nov 13 '05 #12

 P: n/a ww*******@mail2.swjtu.edu.cn (wwj) wrote: [ Don't top-post, please. Corrected. ] "Roose" wrote in message news:... 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. That is, it manages their automatic cleanup after the function exits. 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. 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. 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 Nov 13 '05 #14

 P: n/a wwj wrote: [OT] Please don't top-post (corrected) Bruno Desthuilliers wrote in message news:<3f***********************@news.free.fr>...wwj wrote:Hi ,allI want to know the difference between char a[6] and char *p=newchar[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) and the difference between the heap and the stack,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 Nov 13 '05 #15

 P: n/a wwj wrote: 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. -- Nov 13 '05 #16

 P: n/a Bruno Desthuilliers wrote in message news:<3f***********************@news.free.fr>... wwj wrote: 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 C and C++ 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, in C++ usually the 'new' operator), and that must be freed by code - usually in C with the 'free()' function and in C++ with 'delete'). 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 -- Imanpreet Singh Arora isingh AT acm DOT org Nov 13 '05 #18

 P: n/a te*********@BUSThotmailE.Rcom wrote in message news:<1g3wb6i.120yevw1ji5orwN%te*********@BUSThotm ailE.Rcom>... wwj wrote: 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. -- 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.. -- Imanpreet Singh Arora isingh AT acm DOT org Proud to be a part of c.l.c community. BZzzzzzzzzzzzzzzzzzzzzzzzzzz Nov 13 '05 #19

 P: n/a "Minti" wrote in message news:e8**************************@posting.google.c om... Bruno Desthuilliers wrote in message news:<3f***********************@news.free.fr>... wwj wrote: 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 C and C++ 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 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, in C++ usually the 'new' operator), and that must be freed by code - usually in C with the 'free()' function and in C++ with 'delete'). 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 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 Nov 13 '05 #20

 P: n/a On 4 Nov 2003 02:13:44 -0800, in comp.lang.c , ww*******@mail2.swjtu.edu.cn (wwj) wrote: Ok,thanks Roose very much.You are a good person , goodness. no comment. In our here ,I learn from school that basiclly C++ is a extension ofC,and C is a subset of C++, This is a very badly wrong piece of learning. C is NOT a subset of C++, and nor is C++ an extension of C. They're different languages. expcept some difference.Maybe it is that myteacher do not express that clearly or I do not understand thatclearly.So sorry for everyone ,I wish this post ends the heartrendingtopic,and all not waster time on the confused quarrel. No problem. but please don't take Roose as a good teacher. He's not. -- Mark McIntyre CLC FAQ CLC readme: ----== Posted via Newsfeed.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeed.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= 19 East/West-Coast Specialized Servers - Total Privacy via Encryption =--- Nov 13 '05 #21