Re: [SLUG] c programming - structures
On Mon, 2004-10-18 at 11:21 +1000, torquemada wrote: understanding structures and a knowledge beforehand of what each element is, is essential. dereferencing any pointers might be needed to determine if the structures are identical or not. refer to the data-dictionary for the structure or documentation in that case. one could even hypothetically have a pointer embedded in a structure that points back to the original structure and one might end up in a infinite loop when comparing. but that would be an extreme case. take care and have fun. Thats not particularly extreme or hypothetical. A circular buffer for example, implemented as a list of buffers, is an immediate example. So are any trees with uplinks. Rob -- GPG key available at: http://www.robertcollins.net/keys.txt. signature.asc Description: This is a digitally signed message part -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
Re: [SLUG] c programming - structures
when comparing structures, compare each member.
maybe read some good books on c programming too which
will explain how c programmers use structures. kr comes to mind
using a memcmp or similar as a rule of thumb is useful but
not very much as it won't dereference any elements that are pointers.
so compare each element and member.
cordially
Torquemada
On Sat, 16 Oct 2004, Lucas King wrote:
hello,
how does one compare two structures of the same type?
Anjuta is returning an error when i compile :
if (sin1 == sin2) {
..
..
}
where sin1 and sin2 are structures of the same type. the sin structure
is sockaddr_in.
thanking you in advance,
Lucas
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Re: [SLUG] c programming - structures
On Mon Oct 18, 2004 at 11:02:46 +1000, torquemada wrote: when comparing structures, compare each member. maybe read some good books on c programming too which will explain how c programmers use structures. kr comes to mind using a memcmp or similar as a rule of thumb is useful but not very much as it won't dereference any elements that are pointers. so compare each element and member. Of course it is totally domain specific as to whether it is correct to compare the pointer itself, or the value pointed to. (Which of course could be another struct!) Benno -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
Re: [SLUG] c programming - structures
understanding structures and a knowledge beforehand of what each element is, is essential. dereferencing any pointers might be needed to determine if the structures are identical or not. refer to the data-dictionary for the structure or documentation in that case. one could even hypothetically have a pointer embedded in a structure that points back to the original structure and one might end up in a infinite loop when comparing. but that would be an extreme case. take care and have fun. cordially Torquemada On Mon, 18 Oct 2004, Benno wrote: On Mon Oct 18, 2004 at 11:02:46 +1000, torquemada wrote: when comparing structures, compare each member. maybe read some good books on c programming too which will explain how c programmers use structures. kr comes to mind using a memcmp or similar as a rule of thumb is useful but not very much as it won't dereference any elements that are pointers. so compare each element and member. Of course it is totally domain specific as to whether it is correct to compare the pointer itself, or the value pointed to. (Which of course could be another struct!) Benno -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
[SLUG] c programming - structures
hello,
how does one compare two structures of the same type?
Anjuta is returning an error when i compile :
if (sin1 == sin2) {
..
..
}
where sin1 and sin2 are structures of the same type. the sin structure
is sockaddr_in.
thanking you in advance,
Lucas
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Re: [SLUG] c programming - structures
On Sat Oct 16, 2004 at 16:21:04 +1000, Lucas King wrote:
hello,
how does one compare two structures of the same type?
Anjuta is returning an error when i compile :
if (sin1 == sin2) {
..
..
}
where sin1 and sin2 are structures of the same type. the sin structure
is sockaddr_in.
thanking you in advance,
You need to either compare each element, or use memcp; eg:
if (memcmp(sin1, sin2, sizeof sin1) == 0) {
}
Benno
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Re: [SLUG] c programming - structures
quote who=Benno
On Sat Oct 16, 2004 at 16:21:04 +1000, Lucas King wrote:
how does one compare two structures of the same type?
You need to either compare each element, or use memcp; eg:
if (memcmp(sin1, sin2, sizeof sin1) == 0) {
}
and memcmp isn't usually a great idea, because most structures have padding
bytes that will be uninitialised (random) data.
J.
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Jan Schmidt [EMAIL PROTECTED]
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Re: [SLUG] c programming - structures
Jan Schmidt wrote:
quote who=Benno
On Sat Oct 16, 2004 at 16:21:04 +1000, Lucas King wrote:
how does one compare two structures of the same type?
You need to either compare each element, or use memcp; eg:
if (memcmp(sin1, sin2, sizeof sin1) == 0) {
}
and memcmp isn't usually a great idea, because most structures have padding
bytes that will be uninitialised (random) data.
J.
You can overcome this by memset(3)'ing the struc to zero's when it's
allocated, or use calloc(3).
How usually do you compare structures? Member by member?
C++'s default comparison is at the bit level, how does it overcome
the uninitialized padding problem you pointed?
Cheers,
--Amos
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