Re: q for the C hackers
On Mon, 2003-08-18 at 20:13, Erik Price wrote: However, what is the convention in C? There seem to be two fine ways of doing it -- using the preprocessor, or the const keyword: #define NUMBER_OF_UNITS 8 const int NUMBER_OF_UNITS = 8; Generally, the more the compiler knows, the better it can do it's job, so I usually prefer the latter. There are still some places in C (C99 specifically) where you you have no choice but to use macros, like array declarations. I believe that C++ const variables can be used wherever a simple #define can. aaron BTW, Is there a reason why mailman isn't configured to set the reply-to header? signature.asc Description: This is a digitally signed message part
Re: Raw disk i/o
On Tue, 2003-08-19 at 00:21, Derek Martin wrote: On Mon, Aug 18, 2003 at 11:13:48PM -0400, Jeff Macdonald wrote: Hi, I am trying to understand how one uses raw disk i/o in Linux. I If you're not a filesystem engineer, you probably just really don't want to do this. This is the level at which the filesystem reads and writes data -- it is a raw byte stream. If you write data at this level, you will destroy your filesystem. understand that the i/o skips the kernel buffer. Well, IIRC, unlike most other Unix implementations, Linux disk I/O is /always/ block I/O (i.e. buffered by the kernel) unless you apply patches to the kernel. However, if what you're trying to do is avoid a layer of buffers to increase performance, have a look at memory-mapped I/O. See the man page for mmap(2), and/or a good book on programming on Unix systems. I'd suggest W. Richard Stevens' Advanced Programming in the Unix Environment for starters. I think that he's looking for the same raw i/o that oracle likes so much: http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO/rawdev.html But while you don't have to be writing a filesystem to want this, it's still targeted for a pretty select audience. Have you considered a simple O_DIRECT instead? As the parent post mentions, this may require a patched kernel, depending on your vender and filesystem of choice. XFS has had it for a while, but isn't included in redhat kernels. I still recommend XFS for heavy I/O, as it was designed from the start to be industrial strength. According to the following, redhat kernels don't support O_DIRECT for ext3 either (yet) https://listman.redhat.com/archives/ext3-users/2003-March/msg00114.html aaron signature.asc Description: This is a digitally signed message part
Re: q for the C hackers
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 On Mon, 18 Aug 2003 20:53:01 -0400 Ray Cote [EMAIL PROTECTED] wrote: At 8:13 PM -0400 8/18/03, Erik Price wrote: However, what is the convention in C? There seem to be two fine ways of doing it -- using the preprocessor, or the const keyword: #define NUMBER_OF_UNITS 8 const int NUMBER_OF_UNITS = 8; This tends to be the nicer way to do it these days. Biggest advantage is that you get type checking with a const which you don't get with a #define. Been so long since I used pure C (vs C++) compilers, that I'm not sure whether const ever made it into the C standard, or if it is still a C++ extension. Well supported, though. Works in all the compilers I use. The difference, in C, is that the const keyword was introduced by the ANSI 89 standard. Unlike C++, NUMBER_OF_UNITS (const int) is a variable and may even be altered. In C++, this construct would be a true constant (as Aaron mentions). - -- Jerry Feldman [EMAIL PROTECTED] Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9 -BEGIN PGP SIGNATURE- Version: GnuPG v1.2.2 (GNU/Linux) iD8DBQE/QgoR+wA+1cUGHqkRAljfAJ0ZGX2IQ7ogou/wn6BGs7IDdacRlwCfRFUq zg4UxBnSHaWGHIY+8LLpg3k= =5VN8 -END PGP SIGNATURE- ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
Derek Martin [EMAIL PROTECTED] writes: On Mon, Aug 18, 2003 at 08:13:05PM -0400, Erik Price wrote: However, what is the convention in C? There seem to be two fine ways of doing it -- using the preprocessor, or the const keyword: #define NUMBER_OF_UNITS 8 const int NUMBER_OF_UNITS = 8; Normally, the former way is what you'd use. The latter construct is most often used, in my experience, for function parameters which you want to make sure are not modified by the function to which they belong. This is confused. Erik wasn't even asking about function parameters. He just wants to use a constant in his program. Sure, const carries some meaning when used with function parameters, but Erik wasn't asking about this. I'm not a compiler guru, but I believe references to the #define'd macro will cause the compiler to use immediate mode addressing, using the value of the macro literally, requiring no additional storage beyond what is required to store the opcode and its operands. Whereas the second method allocates storage in the segment of memory associated with initialized data that hangs around, so that it can contain the constant. Like you stated in a later post, exactly *what* the compiler does for these cases is implementation defined. --kevin -- Kevin D. Clark / Cetacean Networks / Portsmouth, N.H. (USA) cetaceannetworks.com!kclark (GnuPG ID: B280F24E) alumni.unh.edu!kdc ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
On Tue, Aug 19, 2003 at 02:50:01AM -0400, Aaron Hope [EMAIL PROTECTED] wrote:
On Mon, 2003-08-18 at 20:13, Erik Price wrote:
However, what is the convention in C? There seem to be two fine ways
of doing it -- using the preprocessor, or the const keyword:
#define NUMBER_OF_UNITS 8
const int NUMBER_OF_UNITS = 8;
Generally, the more the compiler knows, the better it can do it's job,
so I usually prefer the latter. There are still some places in C (C99
specifically) where you you have no choice but to use macros, like array
declarations. I believe that C++ const variables can be used wherever a
simple #define can.
Actually, the following is valid C99:
const int m = 10;
int
foo(int n) {
char s[n];
char t[m];
...
}
BTW, Is there a reason why mailman isn't configured to set the
reply-to header?
Because we don't want it to. Can we not go there again? Convince
your mailer to set Mail-Followup-To, if you'd like (mutt does that).
--
Bob Bell [EMAIL PROTECTED]
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If the only tool you have is a hammer, you tend to see every
problem as a nail.
-- Abraham Maslow
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Re: q for the C hackers
Aaron Hope [EMAIL PROTECTED] writes:
On Mon, 2003-08-18 at 20:13, Erik Price wrote:
However, what is the convention in C? There seem to be two fine ways
of doing it -- using the preprocessor, or the const keyword:
#define NUMBER_OF_UNITS 8
const int NUMBER_OF_UNITS = 8;
Generally, the more the compiler knows, the better it can do it's job,
so I usually prefer the latter. There are still some places in C (C99
specifically) where you you have no choice but to use macros, like array
declarations.
Another possibility is to use enums, i.e.:
enum { BUFSIZE=512 };
char arr[BUFSIZE];
I use this frequently, and I recommend this.
I believe that C++ const variables can be used wherever a
simple #define can.
Well, they can be used for array initialization too.
--kevin
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Re: q for the C hackers
On Tue, Aug 19, 2003 at 09:07:23AM -0400, Kevin D. Clark [EMAIL PROTECTED] wrote:
Another possibility is to use enums, i.e.:
enum { BUFSIZE=512 };
char arr[BUFSIZE];
I use this frequently, and I recommend this.
One advantage of enum's is that symbolic debuggers can display the
symbolic name, instead of just the numeric value, if the data type is
right. We do this in the HP-UX kernel. It even works with bit flags.
It's nice when debugging.
--
Bob Bell [EMAIL PROTECTED]
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Windows 98: n. minor bug-fix/patch release of 32-bit extensions
and a graphical shell for a 16-bit patch to an 8-bit operating
system originally coded for a 4-bit microprocessor, written by a
2-bit company that can't stand 1 bit of competition.
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Re: Reply-To munging (was: q for the C hackers)
On Tue, 2003-08-19 at 09:53, [EMAIL PROTECTED] wrote: To avoid rehashing, here are the two arguments: Reply-To Munging Considered Harmful http://www.unicom.com/pw/reply-to-harmful.html Reply-To Munging Considered Useful http://www.metasystema.org/essays/reply-to-useful.mhtml Thank God for Evolution's 'Reply to List' option! :-) ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
(no subject)
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Re: Raw disk i/o
On Tue, 2003-08-19 at 03:12, Aaron Hope wrote: I think that he's looking for the same raw i/o that oracle likes so much: http://www.tldp.org/HOWTO/SCSI-2.4-HOWTO/rawdev.html Yep. I've also seen this reference. But while you don't have to be writing a filesystem to want this, it's still targeted for a pretty select audience. Have you considered a simple O_DIRECT instead? I'm running 2.6.0-test3 so I think O_DIRECT may be supported. I'm under the assumption that RAW i/o came before memory mapped i/o. Seems RAW uses user space memory while memory mapped uses kernel space memory? Is that right? I also found a paper that showed that RAW was actually slower than EXT3 for a database system. So advantages of RAW: * data is definitely written to disk when write/pwrite returns (what about the disk's cache?) * no extra buffer * no file system overhead Disadvantages: * must read/write in proper block size bytes * no file system - it is just a stream of bytes And to use a raw device: * use raw to associate a block device with a raw device * open() the raw device * read/write to it - use seek to move around Please correct me if I have the wrong idea. I do have Stevens' books and consider them to be my bibles. :-) ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
However, what is the convention in C? There seem to be two fine ways of doing it -- using the preprocessor, or the const keyword: #define NUMBER_OF_UNITS 8 const int NUMBER_OF_UNITS = 8; I'm just interested in hearing about whether one is more appropriate than the other in some contexts. Thanks. I would stick with defines. More modern languages have the option of effectively treating a const declaration as an immediate value, but I do not believe that C can. However there are times when a declaration which allocates storage is necessary, as when you need to pass a pointer to a value. Also, for strings the C standard requires each literal string constant to occupy unique read/write storage (in case the code decides to rewrite part of it). Therefore allocating a (optionally const) variable will use less storage than repeated use of a define'd string constant. Alternatively most compilers provide an option for making string constants read-only. The const type modifier is part of the ANSI/ISO C language standard (as is void and various other post KR enhancements). -dl -- David A. Long JumpShift, LLC [EMAIL PROTECTED] ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Reply-to header, yet again (was Re: q for the C hackers)
On Tue, Aug 19, 2003 at 02:50:01AM -0400, Aaron Hope wrote: BTW, Is there a reason why mailman isn't configured to set the reply-to header? Yes. We've had this holy war before, and the (small) majority of list members were against reply-to. The logical argument: Setting the reply-to header changes the behavior of your mailer, such that it no longer does what it is intended to do when you use the reply function: reply to the sender. Setting the reply-to header makes it impossible for well-behaved mailers to send a private reply to the sender without manually editing the headers. Leaving it out makes it possible for well-behaved mailers to use a list-reply function to respond to the list, when that is what we want to do, or failing that to use the group-reply function, which virtually all mailers have had for centuries now. Setting reply-to also makes it impossible to respond to posters who have themselves set the reply-to header because they NEED it. That's the essence of it, but if you haven't heard enough, there's this: http://www.unicom.com/pw/reply-to-harmful.html People familiar with the argument also know about this: http://www.metasystema.org/essays/reply-to-useful.mhtml In the end, it can be shown that munging reply-to causes some users genuine damage (such as in the case of the guy who needs to set reply-to in order to receive mail), whereas not munging it merely reduces convenience for some people who have sh!tty mailers. The rest of the world shouldn't be punished for your poor choice of software... -- Derek D. Martin http://www.pizzashack.org/ GPG Key ID: 0xDFBEAD02 -=-=-=-=- This message is posted from an invalid address. Replying to it will result in undeliverable mail. Sorry for the inconvenience. Thank the spammers. pgp0.pgp Description: PGP signature
Python notes - the Millenium - published at last
More excuses than memory leaks in a C++ program... :) I apologize for the delay in getting my notes onto the 'net. At last they're available for browsing and download. These notes are exactly what was in the handouts, produced from the same sources. (By a Python program, natch). http://www.in-spec-inc.com/pythontalk.html Comments welcome. -Bill Footnote: incidentally, I've crossed a new horizon since the talk: using Python for development on Winxx, programming Excel and Access, pulling the puppets' strings using COM and ADO. Not my choice to have to do something so ugly, but if one MUST Python makes it almost as easy as opening a file. It just works (tm). Add to suggested reading: _Python Programming on Win32_, Hammond and Robinson, O'Reilly, ISBN 1-56592-621-8. ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: apache serving non-existent pages
The page does not contain any php code, I have just defaulted to the extension because I will incorporate some code in later. My virtual host section of httpd.conf looks as follows: NameVirtualHost * VirtualHost * ServerName derek.homeunix.org DocumentRoot /var/www/html /VirtualHost VirtualHost * ServerName deucedaily.homeunix.org DocumentRoot /var/www/html/html-deuce /VirtualHost As you can see very straight forward. I have since added back in the html-deuce folder, the new domain DocumentRoot. I created another file in there which will not show up. I get a 404 not found, but it still thinks it can find the index, which I renamed to index.php.old, as well as index.html, and that is the only instance of the file on the whole server, unless there is a temporary cached copy someplace. Derek Doucette http://derek.homeunix.org Derek Martin said: On Mon, Aug 18, 2003 at 04:27:23PM -0400, Derek Doucette wrote: The page should look like the one at: http://derek.homeunix.org/deucedaily.php The only difference is with the link at the bottom regarding the E-mail. Is the index at the correct/preferred URL actually generated by a PHP script? If so, perhaps you could post it... If not, perhaps you could post the contents of the actual file? You might also post the virtual host portion of your apache configuration, including any alias sections for it, and any directory directives too. -- Derek D. Martin http://www.pizzashack.org/ GPG Key ID: 0xDFBEAD02 -=-=-=-=- This message is posted from an invalid address. Replying to it will result in undeliverable mail. Sorry for the inconvenience. Thank the spammers. ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Reply-To munging (was: q for the C hackers)
On Tue, 19 Aug 2003, at 2:50am, [EMAIL PROTECTED] wrote: BTW, Is there a reason why mailman isn't configured to set the reply-to header? Some time back, the list took a vote, and more people voted harmful then useful, and we went with the plurality. To avoid rehashing, here are the two arguments: Reply-To Munging Considered Harmful http://www.unicom.com/pw/reply-to-harmful.html Reply-To Munging Considered Useful http://www.metasystema.org/essays/reply-to-useful.mhtml -- Ben Scott [EMAIL PROTECTED] | The opinions expressed in this message are those of the author and do | | not represent the views or policy of any other person or organization. | | All information is provided without warranty of any kind. | ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
Tom Fogal wrote: I'm just interested in hearing about whether one is more appropriate than the other in some contexts. Thanks. Generally, I would use #defines for anything but function parameters. Passing things as a constant reference (const type val) is a good way to avoid passing a large value without the overhead of actual passing it. I understand what you are saying, about passing a reference to something rather than passing the thing itself. My understanding is that this is because the value of a reference is a memory address, which is usually smaller than say, some large value (please correct me if this is incorrect). But why does it have to have const placed there? This seems like it should prevent the value from being modified in the body of the function somehow, but is it required or are you suggesting it as good practice? Unfortunately, references do not exist in C alone (they were introduced in C++) I seem to be confused about the difference between references and a type's address. Are you saying that val is a reference, and that this is different from the address of 'val'? I thought that this meant the address of 'val'. Thanks everyone for contributing to this discussion. Erik ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
Tom Fogal [EMAIL PROTECTED] writes:
the const int way stores the variable in read only memory, and thus, IMO is a
waste of memory. Also, it would be required to do a memory lookup when
accessing the value.
The value *might* get stored in read-only memory. The standard
doesn't require this.
[snip]
Finally, I've never actually heard of 'const' in C. I know that it was
introduced with C++, although i would not be surprised to see later editions
of the C standard included it.
It is not in KR ('the white book'), IIRC.
Unless you're looking at the old testament, I gotta believe its in
there. const most certainly exists in C.
Regards,
--kevin
--
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Re: q for the C hackers
Tom Fogal wrote:
I'm just interested in hearing about whether one is more appropriate
than the other in some contexts. Thanks.
Generally, I would use #defines for anything but function parameters.
Passing things as a constant reference (const type val) is a good way to
avoid passing a large value without the overhead of actual passing it.
I understand what you are saying, about passing a reference to something
rather than passing the thing itself. My understanding is that this is
because the value of a reference is a memory address, which is usually
smaller than say, some large value (please correct me if this is
incorrect). But why does it have to have const placed there? This
seems like it should prevent the value from being modified in the body
of the function somehow, but is it required or are you suggesting it as
good practice?
The bit about memory addresses instead of some large value is entirely correct.
Practically however, this will only be better when passing a value larger than
the register size of the architecture you are on. For instance, on ix86 linux,
all pointers are 32-bit integers. Thus passing a constant reference to another
integer still means you have to pass an integer to the function, thus saving
nothing.
This is commonly used when you have a large record or object.
The const is purely optional; you could just as easily remember yourself that
'hey, i dont want to change that value in this function' and simply not do it.
The justification i was given for such usage is that someone who is not you
can quickly look at the function header/prototype and see, 'oh, this value is
const, it wont change when i pass it to the function'.
Also, supposedly it prevents you from 'forgetting' you didnt mean to change it,
and doing so on accident. IMHO though, if you can't remember you didn't want
to change a fqn parameter, you're functions are wy to long, or you aren't
cut out for the programming vocation :P
Btw, a similar gain can be obtained via pointers, so C programmers aren't
left out =).
Unfortunately, references do not exist in C alone (they were introduced in
C++)
I seem to be confused about the difference between references and a
type's address. Are you saying that
val
is a reference, and that this is different from the address of 'val'? I
thought that this meant the address of 'val'.
Oh yes, this is a source of much confusion. You see, C++ introduced this idea
called a 'reference', which, for all intents and purposes is a pointer, but
you dont have to dereference it as such. thus if i have a procedure that wants
to change its integer parameter to 5, i could do the following in C++:
void change_int(int changeme) { changeme = 5; }
C programmers would flip at such a statement - 'Youll screw everything up! That
makes changeme have whatever is in memory location 5! That could be
ANYTHING!' etc etc.
Well, thats true. In C, changeme means 'the address of changeme'. In C++, the
changeme could mean EITHER 'the address of changeme' OR 'a reference to
changeme'. I've never had a good explanation as to how one could tell which
is meant. It seems to me that if its passed as a function parameter, it is a
reference. Within a function, it means 'address of'. Don't quote me on that.
Another CS major concurs with my interpretation, acutally.. perhaps I got it
right...
In any case, when programming in C only you don't need to worry about such
unwarranted complications (although i'm a bit biased in that i dislike C++ :).
Thanks everyone for contributing to this discussion.
np, my pleasure =)
-tom
Erik
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Re: q for the C hackers
Tom Fogal wrote: The bit about memory addresses instead of some large value is entirely correct. Practically however, this will only be better when passing a value larger than the register size of the architecture you are on. For instance, on ix86 linux, all pointers are 32-bit integers. Thus passing a constant reference to another integer still means you have to pass an integer to the function, thus saving nothing. This is commonly used when you have a large record or object. Okay, that makes sense. Fundamentally, there seems to be little difference between passing a pointer to an object, and passing the address of the variable holding that object's value. I seem to recall that there literally *is* no difference, actually -- a pointer is just the address of a variable IIRC. But I'm glad you confirmed this. The const is purely optional; you could just as easily remember yourself that 'hey, i dont want to change that value in this function' and simply not do it. The justification i was given for such usage is that someone who is not you can quickly look at the function header/prototype and see, 'oh, this value is const, it wont change when i pass it to the function'. I had forgotten about the header/prototype. Yes, it seems desirable to use 'const' in any function declaration that doesn't modify the parameters, as a way of communicating to others that the parameters will not be modified. I will get in the habit of using 'const' in function parameters. (I don't know C++, but let me take a guess at something -- that, in C++ making a passed reference a constant by using 'const' in a function declaration doesn't make any assurances that the object which the reference points to will not be modified, only that the reference itself will not change. In other words, it is much like passing a 'final' reference in Java.) Btw, a similar gain can be obtained via pointers, so C programmers aren't left out =). And this is what I am more used to seeing -- it appears that usually a function will be written to accept a pointer, rather than a value's address, even if they are the same thing. is a reference, and that this is different from the address of 'val'? I thought that this meant the address of 'val'. Oh yes, this is a source of much confusion. You see, C++ introduced this idea called a 'reference', which, for all intents and purposes is a pointer, but you dont have to dereference it as such. I think I'm going to stay away from C++ for the moment, at least until I have a better grip on C and Objective-C. (Coming from a Java perspective, Objective-C seems a little more straightforward to me than C++, esp since it doesn't seem to have changed any of the rules of C.) Thanks again Tom and everyone. Erik ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Apache on RH9 Crashed (Hacked?)
Ok I finally got access to my machine to assess the damage, I am running RH9, Kernel 2.4.20-19.9 and Apache 2.0.40-21.3. Here is the error message I recieved when trying to restard httpd: Stopping httpd:[ OK ] Starting httpd: [Tue Aug 19 17:27:50 2003] [error] VirtualHost _default_:443 -- mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results [ OK ] Im no to great at interpreting this stuff, but I made no changes to my system to cause this error. I had been running stable for roughly 2 weeks with no problems and then Apache started delivery 400's instead of serving up pages. Now I find this... Any ideas? ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
Tom Fogal [EMAIL PROTECTED] writes:
The const is purely optional; you could just as easily remember yourself that
'hey, i dont want to change that value in this function' and simply not do it.
The justification i was given for such usage is that someone who is not you
can quickly look at the function header/prototype and see, 'oh, this value is
const, it wont change when i pass it to the function'.
Also, supposedly it prevents you from 'forgetting' you didnt mean to change it,
and doing so on accident. IMHO though, if you can't remember you didn't want
to change a fqn parameter, you're functions are wy to long, or you aren't
cut out for the programming vocation :P
(Hmm. Maybe I'm not cut out for programming...)
I must politely, but strenuously disagree. const is incredibly
useful.
I can think of this large class library that I had trouble using in
the past, all because the people who implemented it had a bizarre idea
of who owned what memory. Instead of being able to code to a
well-defined interface (and this involves const), I was told to look
at the implementation of each function/method. This was tedious,
inconsistant, and when the underlying implementation changed (and it
didoften...), I found myself debugging code into the wee hours.
In a large project, const is invaluable.
[snip]
Oh yes, this is a source of much confusion. You see, C++ introduced this idea
called a 'reference', which, for all intents and purposes is a pointer, but
you dont have to dereference it as such. thus if i have a procedure that wants
to change its integer parameter to 5, i could do the following in C++:
void change_int(int changeme) { changeme = 5; }
C programmers would flip at such a statement - 'Youll screw everything up! That
makes changeme have whatever is in memory location 5! That could be
ANYTHING!' etc etc.
Well, thats true. In C, changeme means 'the address of changeme'. In C++, the
changeme could mean EITHER 'the address of changeme' OR 'a reference to
changeme'. I've never had a good explanation as to how one could tell which
is meant. It seems to me that if its passed as a function parameter, it is a
reference. Within a function, it means 'address of'. Don't quote me on that.
Another CS major concurs with my interpretation, acutally.. perhaps I got it
right...
I find this to be a bit confused...
1: In C++, if a is a reference to b, then a is ANOTHER NAME FOR
b. THAT'S IT. No magic here.
2: C++ references are different from Java references in that it is
not possible/legal to have a null reference. A lot of people get
hung up on this...
3: C++ references might be implemented in terms of pointers, but you
shouldn't care about this.
There you go.
--kevin
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Re: q for the C hackers
ANSI C allows the implementation to store duplicate strings in the same memory location at runtime. I stand corrected. My claim came from a very old document. The only (draft) version of the ISO standard I have at my finger tips says it is now unspecified. I think my argument still stands though since it is likely some compilers will not do this optimization (assuming it is still unspecified), and probably none will do it across compilation units. One more case where the allocation of a const variable is useful though is when you want to set the values at link time. You can put all these *constants* in one C file and link with the version of your choice. Especially handy for binary-only distributions. -dl -- David A. Long JumpShift, LLC [EMAIL PROTECTED] ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
in the MX record??
I will be hosting a site for someone who has an exchange server set up locally. Mail traffic for the domain needs to end up at that server rather than be hosted on my web server (sendmail). Can I just have the MX record in DNS set to point to their exchange server? Or does the MX record point to my server which redirects via SendMail config? The exchange server has only a dedicated IP address. Jason Kern ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: q for the C hackers
On Tue, 2003-08-19 at 08:46, Bob Bell wrote:
Actually, the following is valid C99:
const int m = 10;
int
foo(int n) {
char s[n];
char t[m];
...
}
Yes, C99 supports variable sized arrays, but that's not always what you
want. They cannot be statically allocated and cannot be initialized.
Consider the following:
const int m = 10;
int buf[m];
int
foo(int n) {
char s[n] = { 0 };
char t[m];
// code
}
% gcc -std=c99 t.c -o t
t.c:2: error: variable-size type declared outside of any function
t.c: In function `foo':
t.c:5: error: variable-sized object may not be initialized
t.c:5: warning: excess elements in array initializer
t.c:5: warning: (near initialization for `s')
aaron
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Re: in the MX record??
On Tue, 19 Aug 2003, Jason Kern wrote: I will be hosting a site for someone who has an exchange server set up locally. Mail traffic for the domain needs to end up at that server rather than be hosted on my web server (sendmail). Can I just have the MX record in DNS set to point to their exchange server? Or does the MX record point to my server which redirects via SendMail config? The exchange server has only a dedicated IP address. As long as their mail server has an IP address that is directly accessible from the WAN, having the MX record point to it should work. If the target system has a valid hostname that one can retrieve by doing a reverse lookup on the IP address, then use that in the MX record - if not, use any A record name that points to that IP address. CNAMEs should not be used in MX records. -- Bill Mullen [EMAIL PROTECTED] MA, USA RLU #270075 MDK 8.1 9.0 There are two kinds of people in the world, those who believe there are two kinds of people in the world and those who don't. - Robert Benchley ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
Re: in the MX record??
You could certainly do it either way you outline, but by far the easiest would be to simply have the MX record point to their mail server. No reason not to do it that way -- since it's pretty much the only time that DNS allows you to separate out a service based on IP, and you might as well take advantage of it. (Gee, wouldn't it be handy if there were a lookup table like DNS for all services? If DNS has an HTTP port assigned, go there, otherwise, port 80. Ah, well...) -Ken I will be hosting a site for someone who has an exchange server set up locally. Mail traffic for the domain needs to end up at that server rather than be hosted on my web server (sendmail). Can I just have the MX record in DNS set to point to their exchange server? Or does the MX record point to my server which redirects via SendMail config? The exchange server has only a dedicated IP address. Jason Kern ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
RE: Apache on RH9 Crashed (Hacked?)
Upon further inspection I found that my system had been hacked. I found multiple directories /tmp/'usernameonmysystem'-orbit (multiple occurances, one for each username) /tmp/ssh1kzaah /tmp/ssh2... I think I know what orbit is, and I never installed it, but running a netstat showed multiple connections to files in these directories. Can anyone ID this root kit so I can begin pinpointing my security hole? Google has turned up something called MAC_Daddy, but documentation is limited. Anyone had experience with this? -Greg -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gregory P. Bonnette Sent: Tuesday, August 19, 2003 12:37 PM To: [EMAIL PROTECTED] Subject: Apache on RH9 Crashed (Hacked?) Ok I finally got access to my machine to assess the damage, I am running RH9, Kernel 2.4.20-19.9 and Apache 2.0.40-21.3. Here is the error message I recieved when trying to restard httpd: Stopping httpd:[ OK ] Starting httpd: [Tue Aug 19 17:27:50 2003] [error] VirtualHost _default_:443 -- mixing * ports and non-* ports with a NameVirtualHost address is not supported, proceeding with undefined results [ OK ] Im no to great at interpreting this stuff, but I made no changes to my system to cause this error. I had been running stable for roughly 2 weeks with no problems and then Apache started delivery 400's instead of serving up pages. Now I find this... Any ideas? ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
RE: Apache on RH9 Crashed (Hacked?)
On Tue, 2003-08-19 at 23:10, Greg Bonnette wrote: Upon further inspection I found that my system had been hacked. I found multiple directories /tmp/'usernameonmysystem'-orbit (multiple occurances, one for each username) /tmp/ssh1kzaah /tmp/ssh2... Um, I'm not denying that your system could have been hacked, but these directories are not the signature of any rootkit I know of. In fact, they are quite normal. The /tmp/username-orbit directories always appear (and are left behind) when username is running the Gnome desktop. Not sure of their exact nature, but they likely have to do with the ORBit or ORBit2 libraries, which I believe are required by Gnome. The /tmp/ssh* directories are the directories where the socket for each user's instance of sshd that is running that has agent forwarding turned on or each instance of ssh-agent that is running on the local system. I think I know what orbit is, and I never installed it, but running a netstat showed multiple connections to files in these directories. Can anyone ID this root kit so I can begin pinpointing my security hole? Google has turned up something called MAC_Daddy, but documentation is limited. Anyone had experience with this? My search for MAC_Daddy on google doesn't turn up anything resembling a rootkit. So, in sum, you definitely could have been cracked, but I think you are barking up the wrong tree. Well, maybe, that is. You may be identifying that a user's password or ssh key has been comprimised, but the evidence doesn't support a rootkit. At least not yet. ;-) Grab chkrootkit from http://www.chkrootkit.org/, build it, and run it as an initial check. One thing that might help us help you determine what's wrong is by posting the virtual host sections of your /etc/httpd/conf/http.conf, as the message does look related to something in that area. Also, do an 'ls -l' on the file to see when it was last modified. Maybe the 'username' user who is/was logged in is the one who changed it. -- -Paul Iadonisi Senior System Administrator Red Hat Certified Engineer / Local Linux Lobbyist Ever see a penguin fly? -- Try Linux. GPL all the way: Sell services, don't lease secrets ___ gnhlug-discuss mailing list [EMAIL PROTECTED] http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss
