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why still use C?

no this is no trollposting and please don't get it wrong but iam very
curious why people still use C instead of other languages especially C++.

i heard people say C++ is slower than C but i can't believe that. in pieces
of the application where speed really matters you can still use "normal"
functions or even static methods which is basically the same.

in C there arent the simplest things present like constants, each struct and
enum have to be prefixed with "struct" and "enum". iam sure there is much
more.

i don't get it why people program in C and faking OOP features(functi on
pointers in structs..) instead of using C++. are they simply masochists or
is there a logical reason?

i feel C has to benefit against C++.

--
cody

[Freeware, Games and Humor]
www.deutronium.de.vu || www.deutronium.tk
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
Nov 13 '05
687 23872
CBFalconer wrote:
glen herrmannsfeldt wrote:
(snip of base 1000 representation of decimal floating point)
The normalization is done in uncompressed (BCD) form, and then
they are converted to the base 1000 form for storage.

If you have ever designed a floating point package you will
realize that normalization takes up the majority of the time. It
needs to be simple, not a major base conversion. Any reasonable form of decimal FP will be based on some flavor of
bcd, possibly 8421, or excess 3, or 2*421, or even bi-quinary.


I haven't actually checked, but rumors are that it only takes a
few gates to convert between the base 1000 representation, and
BCD. It can be done while loading into registers, or even
as part of the ALU, itself.

-- glen
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
Nov 14 '05 #641
"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> writes:
Note that this code is not very general; it doesn't work for e.g.

CHECK_EXPR_TYPE (foo, int(*)[5]);


How about this:

#define CHECK_EXPR_TYPE (expr, type) \
((void) sizeof(((int (*)(type)) 0)(expr)))

I prefer writing it without the (void) though, so that I can use
the macro as part of a constant expression that initializes a
structure:

enum type {
T_NULL,
T_INT,
T_FLOAT
};
struct smember {
enum type type;
const char *name;
size_t offset;
};
#define SMEMBER_FLOAT(s type, member) \
{ T_FLOAT, #member, \
offsetof(stype, member) \
+ 0*CHECK_EXPR_TY PE(&((stype *) 0)->member, const float *) }

struct demo {
float girth;
float curvature;
};
const struct smember demo_members[] = {
SMEMBER_FLOAT(s truct demo, girth),
SMEMBER_FLOAT(s truct demo, curvature),
{ T_NULL }
};

Type checks like this would be easier if the comma operator were
allowed in constant expressions.
Nov 14 '05 #642

On Sun, 21 Dec 2003, Kalle Olavi Niemitalo wrote:

"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> writes:
Note that this code is not very general; it doesn't work for e.g.

CHECK_EXPR_TYPE (foo, int(*)[5]);


How about this:

#define CHECK_EXPR_TYPE (expr, type) \
((void) sizeof(((int (*)(type)) 0)(expr)))


Quite ingenious, I think -- but AFAIK it isn't guaranteed to
be portable. What you're doing, step-by-step, is:

(int (*)(type)) cast something to ptr-to-function-taking-'type'
0 in fact, cast NULL to that ptr-to-func-type
(expr) see if it will accept 'expr' as an argument
sizeof but don't actually evaluate the result
(void) and discard the result of 'sizeof' as well

The problem is that it's not guaranteed possible to "call" a null
pointer, no matter what type it is, no matter what arguments you try
to pass it. So you have undefined behavior *inside* the 'sizeof',
even though it will not be evaluated. As far as I know. Chapter
and verse would be welcome.
Similar problems shoot down this macro:

#define my_broken_offse tof(t, f) ((char *)&((t *)0)->f - (char *)0)

and I'm curious as to what various compilers make of 'sizeof(1/0)',
and whether it's valid C or not. [I think the answer should be
sizeof(int), but I'm not sure it doesn't invoke UB.]

-Arthur

Nov 14 '05 #643
Arthur J. O'Dwyer wrote:
and I'm curious as to what various compilers make of 'sizeof(1/0)',
and whether it's valid C or not.
[I think the answer should be
sizeof(int),
It is.
but I'm not sure it doesn't invoke UB.]


It doesn't.
The division by zero, does not occur.

--
pete
Nov 14 '05 #644
"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> writes:
On Sun, 21 Dec 2003, Kalle Olavi Niemitalo wrote:

"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> writes:
> Note that this code is not very general; it doesn't work for e.g.
>
> CHECK_EXPR_TYPE (foo, int(*)[5]);
How about this:

#define CHECK_EXPR_TYPE (expr, type) \
((void) sizeof(((int (*)(type)) 0)(expr)))


Quite ingenious, I think -- but AFAIK it isn't guaranteed to
be portable. What you're doing, step-by-step, is:

(int (*)(type)) cast something to ptr-to-function-taking-'type'
0 in fact, cast NULL to that ptr-to-func-type
(expr) see if it will accept 'expr' as an argument
sizeof but don't actually evaluate the result
(void) and discard the result of 'sizeof' as well

The problem is that it's not guaranteed possible to "call" a null
pointer, no matter what type it is, no matter what arguments you try
to pass it.


That's OK; this code doesn't call a null pointer. It contains a
subexpression which is a call to a null pointer, but that subexpression
is never evaluated. Undefined behaviour would only result if that
subexpression was evaluated.
Similar problems shoot down this macro:

#define my_broken_offse tof(t, f) ((char *)&((t *)0)->f - (char *)0)


As long as you never invoke that macro, there's no problem.

If however, you invoke it, e.g.

#define my_broken_offse tof(t, f) ((char *)&((t *)0)->f - (char *)0)
struct s { int x; };
int main() {
return my_broken_offse tof(struct s, x);
}

then the subexpression "((t *)0)->f", which in this example becomes
"((struct s *)0)->x" after macro expansion, will get evaluated,
and so the behaviour is undefined.

--
Fergus Henderson <fj*@cs.mu.oz.a u> | "I have always known that the pursuit
The University of Melbourne | of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.
Nov 14 '05 #645
glen herrmannsfeldt wrote:
CBFalconer wrote:
glen herrmannsfeldt wrote:


(snip of base 1000 representation of decimal floating point)
The normalization is done in uncompressed (BCD) form, and then
they are converted to the base 1000 form for storage.

If you have ever designed a floating point package you will
realize that normalization takes up the majority of the time. It
needs to be simple, not a major base conversion.

Any reasonable form of decimal FP will be based on some flavor of
bcd, possibly 8421, or excess 3, or 2*421, or even bi-quinary.


I haven't actually checked, but rumors are that it only takes a
few gates to convert between the base 1000 representation, and
BCD. It can be done while loading into registers, or even
as part of the ALU, itself.


If you show me (in detail) I will believe you. Not before.

--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
Nov 14 '05 #646
> OK, so still between 49.8 and 53.1 equivalent bits for the mantissa,
11.3 bits for the exponent, and 1 for the sign, so 62.1 worst case
and 65.4 best case, for 63.75 average case, or 99.6% efficient.

This reminds me of all the work the authors of the original Fortran
compiler did to generate as efficient object code as possible.
They needed to convince people that Fortran could be used in place
of assembly code, without a significant loss of efficiency.

Personally, I would have been happy with ordinary BCD arithmetic,
in floating point form. It seems to have worked well for calculator
users for many years now.


There are a few constraints, though. For example, the ISO
COBOL 2002 standard specifies that intermediate calculations
be done using 32 decimal digits of precision. 32 digits of BCD
into a 128-bit register leaves very little room for a sign and
exponent.

Mike Cowlishaw
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
Nov 14 '05 #647
> (snip of base 1000 representation of decimal floating point)
The normalization is done in uncompressed (BCD) form, and then
they are converted to the base 1000 form for storage.

If you have ever designed a floating point package you will
realize that normalization takes up the majority of the time. It
needs to be simple, not a major base conversion.

Any reasonable form of decimal FP will be based on some flavor of
bcd, possibly 8421, or excess 3, or 2*421, or even bi-quinary.


I haven't actually checked, but rumors are that it only takes a
few gates to convert between the base 1000 representation, and
BCD. It can be done while loading into registers, or even
as part of the ALU, itself.


Correct. For details, see a summary at:

http://www2.hursley.ibm.com/decimal/DPDecimal.html

Mike Cowlishaw
--
comp.lang.c.mod erated - moderation address: cl**@plethora.n et
Nov 14 '05 #648
"Kalle Olavi Niemitalo" <ko*@iki.fi> wrote in message
news:87******** ****@Astalo.kon .iki.fi...
Type checks like this would be easier if the comma operator were
allowed in constant expressions.


Yes; that's an aggravating restriction.
The main argument for it seems to be to diagnose
int a[20,30];
but with VLAs that has to be allowed anyway in many contexts,
so it seems pointless to keep the restriction.
Nov 14 '05 #649
"Arthur J. O'Dwyer" <aj*@nospam.and rew.cmu.edu> wrote...
and I'm curious as to what various compilers make of 'sizeof(1/0)',
and whether it's valid C or not. [I think the answer should be
sizeof(int), but I'm not sure it doesn't invoke UB.]


There is no undefined behavior, because the / operator is not
executed (the argument of sizeof is not evaluated).
Nov 14 '05 #650

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