I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks
#include <stdio.h>
#include <math.h>
/* create a 3d point struct*/
typedef struct point{
int x,y,z;
};
/* Function declaration*/
float dist(point *, point *);
point add(point *, point *);
void display(point *);
int main(void)
{
point p1,p2,p3;
p1.x=2;p1.y=4;p 1.z=5;
p2.x=5;p1.y=2;p 1.z=6;
printf("\n dist = %f", dist(&p1,&p2));
add(&p1, &p2);
display(&p3);
return;
}
float dist(point *a, point *b)
{
float length=0.0;
length = sqrt( (a->x-b->x)*(a->x-b->x)+ (a->y-b->y)*(a->y-b->y)+
(a->z-b->z)*(a->z-b->z));
return length;
}
point add(point *a, point *b)
{
point temp;
temp.x=a->x + b->x;
temp.y=a->y + b->y;
temp.z=a->z + b->z;
return temp;
}
void display(point *a)
{
printf("\npoint = %d,%d,%d\n",a->x,a->y,a->z);
}
Feb 22 '07
39  3123 
In article <11************ **********@h3g2 000cwc.googlegr oups.com>,
santosh <sa*********@gm ail.comwrote:
>This doesn't have anything much to do with gcc. Before gcc was
thought of, unix needed -lm to link the maths library, and today the
Mac I'm using doesn't need -lm even though its compiler is gcc.
>Are you sure about the latter? I tried a small test program that
computes sqrt(2.0) and it didn't require "-lm" because gcc was smart
enough to compute the value at compilation time.
>Yes, I made exactly that mistake - I even used sqrt(2.0).
>Try something like
sqrt(time(NULL )); it's a silly thing to compute, but it should prevent
the compiler from optimizing away the sqrt() call.
But in fact that still works without -lm.
>Then either the compiler has an intrinsic for sqrt or else the latter
is present in the same library that contains the non-math standard C
functions. Also maybe the environment is secretly supplying the
library option?
Foiled again, it's using an inline instruction for sqrt. So this time
I changed it to tgamma(time(0)) , on the assumption that not even the
latest Intel processors have a gamma instruction, and it *still*
doesn't need -lm. Looking at the output of gcc -S and gcc -v, it
appears to be calling a function and linking to a library "-lSystem",
which includes the maths functions.
-- Richard
--
"Considerat ion shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
Good evening,
On 2007-02-23, jacob navia <ja***@jacob.re mcomp.frwrote:
Nils Weller a écrit :
>On 2007-02-22, jacob.navia <ja***@jacob.re mcomp.frwrote:
>>>
We have often discussed here this msfeature of gcc but they will never
change it as it seems.
You cannot remove historical quirks like this without breaking
anything, especially if they've been almost universial practice
for a couple of decades. I've considered adding -lm by default
to my compiler as well, but I figured this would end up doing
the users a disservice. Because if you write build scripts for
a compiler which does not require you to link that library
explicitly, then chances are your project will break if you
use it with a different compiler.
Wrong!
They would say
What a bad compiler this one. It needs an explicit -lm switch.
Well, they may not appreciate it, but it would be "for their own
good". ;-)
This isn't a big deal anyway because compilers are already
incompatible in lots of other ways, and I can see where you're
coming from. But myself I would prefer to be warned about such
potential problems, and I can see good reasons for not changing
this particular oddity.
(It would also be nice to get warnings about functions with
dangerously nonportable semantics, such as the signal()
function which is still broken on most System V derivatives,
but that's another story ...)
And the builders of the other compiler would say
Mmmm many users are complaining that the xxx compiler does NOT
need the -lm switch... Should we include it by default?
Yes, this is not a fortunate situation. But you see, there is so
much existing practice that you can't get everyone to change this
without running into new problems. That's all I was saying. If
you get gcc to change, you'd still have to get lots and lots of
other Unix compilers to change, and lots of users to update their
gcc versions.
>It's not just compilers by different vendors that would be
affected, but also older versions of a compiler that recently
abandoned this requirement. If gcc comes out with a new
release that always links with that library by default, as you
you suggest, then code developed with that compiler version is
more likely not to build with older versions.
So what?
That would impose another implicit (and probably unexpected)
compiler version dependency on your software. The confusion would
be shifted from the developer to the end users, who you shouldn't
expect to have the most up-to-date compiler version available to
compile your stuff.
That would suck.
I have given also much thought to this, and I have developed a
database that is used by the IDE. When it detects a message like
"undefined external reference" it wil look at the database and
propose the libraries to the user...
Good!
I am working with AIX version too. Great system but needs some
more user friendliness.
True. Would also have been nice if it didn't force all-position-
independent code down everyone's throat.
--
Nils R. Weller, Bremen (Germany)
My real email address is ``nils<at>gnuli nux<dot>nl''
.... but I'm not speaking for the Software Libre Foundation!
Richard Tobin wrote:
In article <11************ **********@h3g2 000cwc.googlegr oups.com>,
santosh <sa*********@gm ail.comwrote:
This doesn't have anything much to do with gcc. Before gcc was
thought of, unix needed -lm to link the maths library, and today the
Mac I'm using doesn't need -lm even though its compiler is gcc.
Are you sure about the latter? I tried a small test program that
computes sqrt(2.0) and it didn't require "-lm" because gcc was smart
enough to compute the value at compilation time.
Yes, I made exactly that mistake - I even used sqrt(2.0).
Try something like
sqrt(time(NULL) ); it's a silly thing to compute, but it should prevent
the compiler from optimizing away the sqrt() call.
But in fact that still works without -lm.
Then either the compiler has an intrinsic for sqrt or else the latter
is present in the same library that contains the non-math standard C
functions. Also maybe the environment is secretly supplying the
library option?
Foiled again, it's using an inline instruction for sqrt. So this time
I changed it to tgamma(time(0)) , on the assumption that not even the
latest Intel processors have a gamma instruction, and it *still*
doesn't need -lm. Looking at the output of gcc -S and gcc -v, it
appears to be calling a function and linking to a library "-lSystem",
which includes the maths functions.
Hmm..., curious system, (which one?.) This is a case in point for the
argument to keep this group loosely bound to ISO C.
On Fri, 23 Feb 2007 17:58:11 +0100, in comp.lang.c , jacob navia
<ja***@jacob.re mcomp.frwrote:
>That is why no progress is done in unix... Old bugs are preserved
for posterity.
right - that'll be why unix and unix clones are so unsuccessful then.
>The "make" utility needs a tab as the first char
in an action line. If you put spaces it will not recognize the
line
Apparently you have a /really/ old version of make.
>This BUG has been in all unices since at least 1983,
A bug is when something doesn't behave like its supposed to. Ever used
a fortran compiler? Rry sticking a C character at column seven. Theres
a bug that means it skips that line, apparently.
As it happens, I think the need to put -lm in on some versions of gcc
and some osen is a bit annoying, but its hardly a bug, any more than
having to use vi is a bug, or some versions of SQL not liking iif()
statements. Its just How That Platform Works (tm).
--
Mark McIntyre
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan
In article <11************ **********@s48g 2000cws.googleg roups.com>,
santosh <sa*********@gm ail.comwrote:
>Foiled again, it's using an inline instruction for sqrt. So this time
I changed it to tgamma(time(0)) , on the assumption that not even the
latest Intel processors have a gamma instruction, and it *still*
doesn't need -lm. Looking at the output of gcc -S and gcc -v, it
appears to be calling a function and linking to a library "-lSystem",
which includes the maths functions.
>Hmm..., curious system, (which one?.)
Just a current Mac.
-- Richard
--
"Considerat ion shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
jacob navia <ja***@jacob.re mcomp.frwrites:
Nils Weller a écrit :
>On 2007-02-22, jacob.navia <ja***@jacob.re mcomp.frwrote:
>>We have often discussed here this msfeature of gcc but they will
never change it as it seems.
You cannot remove historical quirks like this without breaking
anything, especially if they've been almost universial practice
for a couple of decades. I've considered adding -lm by default
to my compiler as well, but I figured this would end up doing
the users a disservice. Because if you write build scripts for
a compiler which does not require you to link that library
explicitly, then chances are your project will break if you
use it with a different compiler.
Wrong!
They would say
What a bad compiler this one. It needs an explicit -lm switch.
And the builders of the other compiler would say
Mmmm many users are complaining that the xxx compiler does NOT
need the -lm switch... Should we include it by default?
Oh, no, I have to type an extra 3 characters!
Most C compilers are not conforming by default; you have to specify
extra options to make then conform to the standard. I agree that the
need for "-lm" is annoying, but I just don't worry about it that much.
>In that case the time you have to deal with this problem is
just deferred until a later date. So I think it's best to have
to encounter, recognize, and fix this problem as early as
possible.
That is why no progress is done in unix... Old bugs are preserved
for posterity. The "make" utility needs a tab as the first char
in an action line. If you put spaces it will not recognize the
line and say:
Missing separator in rules. Stop.
This BUG has been in all unices since at least 1983, when I saw the
first one, and was bitten by this bug.
So you haven't actually been bitten by it since 1983? And what does a
misfeature in "make" have to do with C?
(I don't know whether correcting this might break some existing
Makefiles. Discuss in comp.unix.progr ammer if you're interested.)
>It's not just compilers by different vendors that would be
affected, but also older versions of a compiler that recently
abandoned this requirement. If gcc comes out with a new
release that always links with that library by default, as you
you suggest, then code developed with that compiler version is
more likely not to build with older versions.
So what?
So code developed with that compiler version is more likely not to
build with older versions.
[...]
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
Mark McIntyre <ma**********@s pamcop.netwrite s:
On Fri, 23 Feb 2007 17:58:11 +0100, in comp.lang.c , jacob navia
<ja***@jacob.re mcomp.frwrote:
>>That is why no progress is done in unix... Old bugs are preserved
for posterity.
right - that'll be why unix and unix clones are so unsuccessful then.
>>The "make" utility needs a tab as the first char
in an action line. If you put spaces it will not recognize the
line
Apparently you have a /really/ old version of make.
[...]
<OT>
Not necessarily. GNU Make 3.81, the latest version, is less than a
year old. (It at least suggests using a tab rather than 8 spaces.)
</OT>
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
On Thu, 22 Feb 2007 12:35:49 -0600, user923005 wrote
(in article <11************ **********@t69g 2000cwt.googleg roups.com>):
On Feb 22, 10:20 am, "DanielJohn son" <diffuse...@gma il.comwrote:
>>Under most UNIX systems, the math library is seperate and not linked
in by default. Add the '-lm' command line switch, (without the
quotes), to cc when you compile it.
>>>Is math.sqrt() correct or just sqrt()
>>The latter, with an argument. The former is C++.
Thanks it worked. Do I always need to compile using -lm switch. I was
completely unawre if this.
How did you miss this when you read the C-FAQ:
14.3: I'm trying to do some simple trig, and I am #including <math.h>,
but I keep getting "undefined: sin" compilation errors.
A: Make sure you're actually linking with the math library. For
instance, under Unix, you usually need to use the -lm option, at
the *end* of the command line, when compiling/linking. See also
questions 13.25, 13.26, and 14.2.
You will notice that it doesn't actually answer his question.
Specifically, "Do i always" ...
And the answer is no, but if you are using any of the math functions
which require it, then yes obviously for a given program.
--
Randy Howard (2reply remove FOOBAR)
"The power of accurate observation is called cynicism by those
who have not got it." - George Bernard Shaw
On Thu, 22 Feb 2007 17:39:04 -0600, Mark McIntyre wrote
(in article <97************ *************** *****@4ax.com>) :
On Thu, 22 Feb 2007 22:12:48 +0100, in comp.lang.c , "jacob.navi a"
<ja***@jacob.re mcomp.frwrote:
>DanielJohnso n a écrit :
>>Thanks it worked. Do I always need to compile using -lm switch. I was
completely unawre if this.
We have often discussed here this msfeature of gcc but they will never
change it as it seems.
Its not a gcc-ism, please don't mischaracterise it. You're probably
aware that all DOS compilers exhibited this same feature for many
years. I think some early Windows ones even did it (certainly C6 and
Watcom's C compiler did, even when compiling windows-compatible code).
The reason, as far as I recall, is their roots in hardware that didn't
provide floating point support.
You had the option to pick what type of math implementation you wanted
to link against, software fp emulation, 8087, Weitek, 68881/2, etc. I
wonder if lcc-win32 can generate code for a Weitek coprocessor?
--
Randy Howard (2reply remove FOOBAR)
"The power of accurate observation is called cynicism by those
who have not got it." - George Bernard Shaw
Randy Howard wrote:
On Thu, 22 Feb 2007 17:39:04 -0600, Mark McIntyre wrote
><ja***@jacob.r emcomp.frwrote:
>>DanielJohns on a écrit :
Thanks it worked. Do I always need to compile using -lm switch.
I was completely unawre if this.
We have often discussed here this msfeature of gcc but they will
never change it as it seems.
Its not a gcc-ism, please don't mischaracterise it. You're probably
aware that all DOS compilers exhibited this same feature for many
years. I think some early Windows ones even did it (certainly C6
and Watcom's C compiler did, even when compiling windows-compatible
code). The reason, as far as I recall, is their roots in hardware
that didn't provide floating point support.
You had the option to pick what type of math implementation you
wanted to link against, software fp emulation, 8087, Weitek,
68881/2, etc. I wonder if lcc-win32 can generate code for a
Weitek coprocessor?
I doubt it. It won't run on a 486 (at least the debugger portion).
--
<http://www.cs.auckland .ac.nz/~pgut001/pubs/vista_cost.txt>
<http://www.securityfoc us.com/columnists/423>
"A man who is right every time is not likely to do very much."
-- Francis Crick, co-discover of DNA
"There is nothing more amazing than stupidity in action."
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