floor()

[Andre]

Trying to use floor in a short progrm, using gcc version 4.5.1 20100924
(Red Hat 4.5.1-4) (GCC)
But compilation keep returning
/tmp/cca35RWE.o: In function `main':
testUTC.c.text+0xa8): undefined reference to `floor'
collect2: ld a retourné 1 code d'état d'exécution
Any idea where to look??
Many thanks
André
BTW: I am retired and doing somme progr for fun )
also using floor, extrated from same progrme works with PICC for pic16f..
CU

 

[Xavier Roche]

testUTC.c.text+0xa8): undefined reference to `floor'

This is Linux specific (not specifically related to C). You need the "m"
library (math) on Linux.

See:
<http://www.kernel.org/doc/man-pages/online/pages/man3/floor.3.html>
"Link with -lm"

gcc ... -lm

 

[Noob]

Trying to use floor in a short progrm, using gcc version 4.5.1
20100924 (Red Hat 4.5.1-4) (GCC) But compilation keep returning
/tmp/cca35RWE.o: In function `main': testUTC.c.text+0xa8):
undefined reference to `floor'

cf. comp.lang.c FAQ list
Question 14.3
http://c-faq.com/fp/libm.html

Q: I'm trying to do some simple trig, and I am #including <math.h>,
but the linker keeps complaining that functions like sin and cos are
undefined.

A: Make sure you're actually linking with the math library. For
instance, due to a longstanding bug in Unix and Linux systems, you
usually need to use an explicit -lm flag, at the end of the command
line, when compiling/linking.

 

[Andre]

Le 01/08/2012 14:38, Xavier Roche a écrit :

This is Linux specific (not specifically related to C). You need the "m"
library (math) on Linux.

See:
<http://www.kernel.org/doc/man-pages/online/pages/man3/floor.3.html>
"Link with -lm"

gcc ... -lm

Many thanks
André

 

[Andre]

Le 01/08/2012 16:47, Noob a écrit :

cf. comp.lang.c FAQ list
Question 14.3
http://c-faq.com/fp/libm.html

Q: I'm trying to do some simple trig, and I am #including<math.h>,
but the linker keeps complaining that functions like sin and cos are
undefined.

A: Make sure you're actually linking with the math library. For
instance, due to a longstanding bug in Unix and Linux systems, you
usually need to use an explicit -lm flag, at the end of the command
line, when compiling/linking.

many thanks
André

 

[Eric Sosman]

I am assuming you are unfamiliar with some of the libraries.

I would suggest a Google search on: C STL floor function

First seven hits are for C++, eighth is for the mythical
language "C/C++", ninth is for C++, tenth is a pediatrician.

I am guessing you haven't added this library which defines the floor
function:

#include <cmath>

I'm confident you're trying to help, but you seem not to
have noticed that the question was about C, not about C++. In
particular, there's no <cmath> header in C.

 

[James Kuyper]

With all due respect, you apparently did not notice this is a "C"
forum, and should have been posted in a "C++" forum then...

Why? The only C++ content in his message was either quoted from your
inappropriate response, or was part of his explanation of why your
response was inappropriate. Precisely because C++ would be on-topic in
such a forum, such a message would NOT be on-topic there.

 

[Andre]

Le 01/08/2012 14:38, Xavier Roche a écrit :

This is Linux specific (not specifically related to C). You need the "m"
library (math) on Linux.

See:
<http://www.kernel.org/doc/man-pages/online/pages/man3/floor.3.html>
"Link with -lm"

gcc ... -lm

I must have missed something as it compile Ok but result of floor(2.233)
is 0??

#include <stdio.h>
#include <math.h>


/**************/
main(argc,argv)
int argc;
char *argv[];
{
int UTC;
double heure;
float minute;
double rst;
int hx;

printf("%d\n\r",floor(2.2333));


}
/*****/

gcc testUTC.c -o heure -lm


../heure
0

 

[Ike Naar]

I must have missed something as it compile Ok but result of floor(2.233)
is 0??

#include <stdio.h>
#include <math.h>

/**************/
main(argc,argv)
int argc;
char *argv[];
{
int UTC;
double heure;
float minute;
double rst;
int hx;

printf("%d\n\r",floor(2.2333));

Type mismatch; floor returns a double, but the
"%d" format expects an integer.

 

[Heinrich Wolf]

....

I must have missed something as it compile Ok but result of floor(2.233)
is 0??

#include <stdio.h>
#include <math.h>


/**************/
main(argc,argv)
int argc;
char *argv[];
{
int UTC;
double heure;
float minute;
double rst;
int hx;

printf("%d\n\r",floor(2.2333));

My Borland C++Builder 5 tells the prototype
double floor(double x);
So your printf has a wrong format string. You should code
printf("%1.0f\n\r",floor(2.2333));

 

[James Kuyper]

That said, I am fully aware that that this is a "C" forum, and as
indicated in my response, I searched with "C" as a parameter.

You may have been aware of it, but nothing you wrote in your response
reflected that awareness, other than the use of C in your recommended
search string. However, your use of STL in that same string negates
that. Since STL is commonly used as an abbreviation for the Standard
Template Library which eventually became a major part (but NOT the
entirety) of the C++ standard library, adding STL to the search
virtually guarantees exclusion of C-specific web sites.

....

And the website I listed is a C programming support site.

No, it's a C and C++ programming site, which like many such sites, does
not do a good job of dealing with the differences between C and C++. In
particular, the particular page you cited documents exclusively the C++
version of the floor() function.

I checked, and most of the pages at that site for other standard library
functions document both the C and the C++ header file name, so it was
just bad luck that the page for floor() does not.

So, if you have a problem with my response, perhaps you should really
take it up with the website referenced.

The last paragraph of your original message was written entirely by you.
Neither of the mistakes in that paragraph was the responsibility of
anyone other than yourself, and that paragraph could not have been
written by someone who was, as you claim to have been, 'fully aware that
this is a "C" forum'.

 

[Eric Sosman]

That said, I am fully aware that that this is a "C" forum, and as
indicated in my response, I searched with "C" as a parameter.

Then why did you offer a C++ answer? (As it happens, even
if the O.P. had been using C++ your answer would not have helped;
his problem was not with compilation, but with linking.)

One of the bigger problems today is that many of the newer compilers
are not strictly "C" systems.

Not sure what you mean by this, or why it would matter. If
Compiler X conforms imperfectly to the C Standard, does it then
make sense to answer as if for COBOL?

And the website I listed is a C programming support site.

No; the web site's *title* says its about C. But the site
itself is not! Here's the code from the page you linked to:

//Example will output 5.9 rounded down
#include <cmath>
#include <iostream>

using namespace std;

int main()
{
cout<<"5.9 rounded down: "<<floor(5.9);
}

So, if you have a problem with my response, perhaps you should really
take it up with the website referenced.

First, it wasn't very smart of you to offer a link to a
poor-quality web site. (The site may have other fine qualities,
but for the question at hand its quality is poor.) Second, your
own text in the body of your own message -- something you can't
blame on a web site -- was a C++ answer, not applicable to C.

Disclaimer: Have a FLAME. Take it to somebody who cares! Here's your
sign... "I am stupid!" , Jeff Foxworthy

Earlier I wrote that I thought you were trying to be helpful.
I'm starting to doubt myself.

 

[Keith Thompson]

printf("%d\n\r",floor(2.2333));

[...]

Apart from the type mismatch, the "\r" is not necessary. Printing
"\n" to a text stream will emit whatever is needed to mark the end
of a line.

 

[Ben Pfaff]

printf("%d\n\r",floor(2.2333));

[...]

Apart from the type mismatch, the "\r" is not necessary. Printing
"\n" to a text stream will emit whatever is needed to mark the end
of a line.

Furthermore, when both \r and \n are used, the normal order is
\r\n (CR LF, not LF CR).

 

[James Kuyper]

printf("%d\n\r",floor(2.2333));

[...]

Apart from the type mismatch, the "\r" is not necessary. Printing
"\n" to a text stream will emit whatever is needed to mark the end
of a line.

Furthermore, when both \r and \n are used, the normal order is
\r\n (CR LF, not LF CR).

According to <http://en.wikipedia.org/wiki/Newline>, LF+CR is used for
"Acorn BBC and RISC OS spooled text output".

 

[Ben Pfaff]

[...]
printf("%d\n\r",floor(2.2333));
[...]

Apart from the type mismatch, the "\r" is not necessary. Printing
"\n" to a text stream will emit whatever is needed to mark the end
of a line.

Furthermore, when both \r and \n are used, the normal order is
\r\n (CR LF, not LF CR).

According to <http://en.wikipedia.org/wiki/Newline>, LF+CR is used for
"Acorn BBC and RISC OS spooled text output".

I stand by my claim about "normal" order. I admit that there may
be systems that use an abnormal order.

 

[Edward A. Falk]

Type mismatch; floor returns a double, but the
"%d" format expects an integer.

Oh, and get rid of the '\r' in the format string. The
C stdio library will handle line endings correctly for
you.

 

[Noob]

I stand by my claim about "normal" order. I admit that there may
be systems that use an abnormal order.

The problem with "norms" is that they are moving targets ;-)

 

[Jorgen Grahn]

Type mismatch; floor returns a double, but the
"%d" format expects an integer.

Might as well mention this: turn on more warnings from the compiler
to avoid such errors. For gcc it's something like

-W -Wall -pedantic -ansi -g -O2

/Jorgen

 

[Jorgen Grahn]

I stand by my claim about "normal" order. I admit that there may
be systems that use an abnormal order.

Or /have been/ in this case. I haven't heard about Acorn for 20 years.

/Jorgen